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WHAT EVOLUTION IS 


LONDON : HUMPHREY MILFORD 
OXFORD UNIVERSITY PRESS 


~ FEB? ry 1926. 






WHAT EVOLUTI 


BY | 
GEORGE HOWARD PARKER 


Professor of Zotlogy and Director of the Zoblogical 
Laboratory, Harvard University 





CAMBRIDGE 
HARVARD UNIVERSITY PRESS 


1926 


COPYRIGHT, 1925, 
BY HARVARD UNIVERSITY PRESS 


Second Printing. 


PRINTED IN THE 
UNITED STATES OF AMERICA 


PREFACE 


THE growing popular interest in evo- 
lution calls for a simple statement 
concerning this doctrine. Such a 
statement should be as brief as is con- 
sistent with right understanding, and 
should be to the point. In view of the 
animated and heated discussions that 
have been excited by the present situ- 
ation, this statement should be free 
from prejudice and partiality. It is 
from this standpoint that the follow- 
ing pages have been written. 

No fundamental doctrine such as 
that of evolution can be rightly con- 
sidered without taking into account 
its full bearings on the whole of or- 
ganic nature. Plants and animals, 
with all their intricate interrelations, 
afford the materials for this theme. 
Man as the most complex of animals 


vi PREFACE 


must find his nature elucidated 
through evolution if this doctrine is 
to maintain itself. What its value is 
in this respect must be judged by 
each reader. 

That the illustrative examples and 
other like materials in the present vol- 
ume are chiefly from zoological 
sources is due to the fact that the 
writer is a zoologist. It is scarcely 
necessary to add that botanical ma- 
terials afford the same kind of evi- 
dence as that given in the body of 
this text and might have been utilized 
in the same way that the zoological 
examples have been. 

It is the object of this volume to 
present a brief, readable account of 
the main facts of evolution, that the 
ordinary reader may acquaint him- 
self with what may be called the ele- 
ments of the subject. That so large a 
topic as evolution can be adequately 


PREFACE Vii 


treated in a volume of the size of the 
present one is quite inconceivable, 
and yet such an account as that which 
follows may at least outline the sub- 
ject and in this way prepare the 
reader for further inquiry. 





WEE 


IV. 


VI. 


CONTENTS 


INTRODUCTORY . 


ee LISTORICAL 


EVIDENCE ON EVOLUTION 


2 


ee 


6. 


From Comparative Anat- 

OLY eaten) aoe ile 
From Embryology . 
From Geology 
From Zoogeography . 
From Rudimentary Or- 

gans . aeons 
Conclusion 


FACTORS IN EVOLUTION 


Ls 


SPSL C ee SS 


Prefatory 

Lamarckism 
Lamarckism mitcieds 
Darwinism ; 
Darwinism eed 
The Mutation Theory . 


HuMAN APPLICATIONS 


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INTRODUCTORY 


EVOLUTION is a term that has been 
used in a great variety of ways. We 
speak of the evolution of the stars, 
meaning thereby the process by which 
stars have grown from gaseous masses 
to incandescent bodies, such as our 
sun, and finally to the cold inert con- 
ditions of stellar death. We speak of 
the evolution of the earth, in that we 
picture the growth of that body as a 
part of the solar system whose central 
element, the sun, yields the energy by 
which the earth is moulded. Under 
the varying heat of this luminary our 
atmosphere is made to move as wind, 
water is evaporated and condensed, 
continents are eroded and dissected, 
materials are disintegrated, trans- 
ported, and deposited—in short, the 
surface of the earth is put under con- 


4 WHAT EVOLUTION IS 


tinual flux and change. Thus the 
present configuration of oceans and 
of continents, of mountains and of 
abysses, is looked upon, not as some- 
thing stationary, but as due to opera- 
tions whose titanic energies have been 
exerting themselves through untold 
ages in the past and will continue so 
to act far into the futures) these 
happenings, and such as occur among 
the stars, constitute what may be 
called cosmic evolution, a body of 
change which in the nature of things 
preceded life and was, in a certain 
sense, preparatory to it. It is the 
plan of this book, not to deal with 
this type of evolution, notwithstand- 
ing the fact that cosmic evolution is 
intimately bound up with the origin 
of living things, but to consider ex- 
clusively the kind of evolution that 
has to do with organisms, with plants 
and animals. Such a type of evolu- 


WHAT EVOLUTION IS 5 


tion may be called organic, as con- 
trasted with what has just been 
spoken of as cosmic. 

Organic evolution, dealing as it 
does with living organisms, has a set 
of problems quite its own. Although 
the body of a plant or of an animal 
contains no chemical element not 
found in the earth, and the energy in 
such living bodies is subject to the 
same laws that govern the inorganic, 
plants and animals have superim- 
posed upon their fundamental cosmic 
properties, other properties more or 
less peculiar to themselves. Thus all 
plants and animals, like other bodies 
about us, are subject to the law of 
gravitation and to other laws of a 
purely physical and chemical nature; 
yet these plants and animals grow, 
reproduce, react, and respond in ways 
which are not entirely consonant 
with the chemistry and physics of the 


6 WHAT EVOLUTION IS 


strictly inorganic. They have, in ad- 
dition to the chemistry and physics 
of lifeless nature, a chemistry and 
physics more or less their own. It is 
in this way that organic evolution 
differs from simple cosmic evolution, 
for organic evolution is a general op- 
eration among plants and animals 
some aspects of which are not to be 
met with in the inorganic. 

Organic evolution, though a well- 
unified field in biology, can be profit- 
ably treated under two heads. ‘The 
first of these has to do with the doc- 
trine of descent with modification — 
the belief that plants and animals of 
particular kinds have descended by 
gradual modification from preéxist- 
ing plants and animals of very dif- 
ferent kinds. This belief, which is 
often spoken of as if it were the 
whole of evolution, is supplemented 
by what may be treated under a sec- 


WHAT EVOLUTION IS 7 


ond heading, a group of doctrines 
that have to do with the way in which 
descent with modification has been 
accomplished. Granting that plants 
and animals have arisen by the modi- 
fication of earlier forms, what have 
been the driving forces in nature that 
have induced this modification? This 
is a newer and much less certain field 
of work than that which deals with 
the simple fact of change or trans- 
mutation in organisms. It includes 
a consideration of Lamarckism, of 
Darwinism or the theory of natural 
selection and such subordinate theo- 
ries as sexual selection, of orthogene- 
sis, of the mutation theory, and of a 
host of other views which from time 
to time have been advanced as ex- 
planations of descent with modifica- 
tion. In the following pages, after 
some brief historical comment, the 
subject matter will be dealt with 


WA 


8 WHAT EVOLUTION IS 


under the two general headings just 
mentioned: evolution as descent with 
modification, and the explanations 
that have been offered for this 
process. 


II 
HISTORICAL 


4 

- 
1 
1 


é 


—, 





HISTORICAL 


THE idea of evolution is often looked 
upon as a comparatively modern one. 
As a matter of fact, it reaches back 
into remote antiquity. Most races of 
primitive man believed in some vague 
way that they had kinship with the 
lower animals. Many of the clans of 
American Indians used animals as 
their totems. Among the Indians of 
the northwest coast the bear, the 
raven, and the beaver were used in 
this way, and in New England the 
wildcat, the wolf, the muskrat, the 
squirrel, the porcupine, and the frog 
were similarly employed. Although 
these totems were primarily signs of 
the clan and were used as such, par- 
ticularly in religious observances, 
they were in many instances invested 
with an ancestral aura, and the clan 


12 WHAT EVOLUTION IS 


was supposed in some vague way to 
have descended from the animal con- 
cerned. Most primitive human be- 
ings seem to have had some such 
traditions as these about animals, but, 
of course, in no case could these views 
be said to have more than remotely 
implied an evolutionary conception. 
They merely show that in primitive 
man kinship with animals was not an 
unknown idea. 

To certain Greeks organic evolu- 
tion in the modern sense came nearer 
to being a reality. Thus the great 
physical philosopher of the Ionian 
School, Anaximander (611-547 B.c.), 
is credited with having held to a 
form of general evolution in which 
man was especially involved. Anaxi- 
mander was apparently impressed 
with the inability of man in his early 
stages of life to care for himself, and 
was thereby led to conclude that 


WHAT EVOLUTION IS 13 


human beings in the beginning must 
have been very different from what 
they are at present. He is even be- 
lieved to have assumed for them an 
aquatic ancestry, perhaps fish-like 
in character. Anaximander’s views 
were often quoted, and thus classical 
antiquity must have had some idea of 
the evolutionary doctrine. 

But the serious advances in this 
body of opinion date from the last 
two centuries. Throughout the early 
part of this period uncertain rumors 
of an evolutionary kind were contin- 
ually heard; and as time went on, 
these rumors ‘became more and more 
distinct. With this growth in defi- 
niteness opposition took on a more 
final shape. Thus Linneus (1707- 
1778), who may be said to have es- 
tablished systematics by publishing 
in his “Systema Naturz” a classifi- 
cation and description of all plants 


14 WHAT EVOLUTION IS 


and animals known in his time, be- 
lieved firmly in the immutability of 
species and declared in favor of the 
biblical account of special creation. 
According to him there are as many 
different species of plants and of an- 
imals on the earth as there were dif- 
ferent forms created by the Supreme 
Being in the beginning. This view, 
based upon the account in Genesis, 
was thus set in strong contrast with 
that of the origin of species through 
descent with modification. 

The first radical exponent of mod- 
ern organic evolution was Lamarck 
(1744-1829) who published in 1809 
his “Philosophie Zoologique.” In 
this volume Lamarck set forth a plea 
that the plants and animals of to-day 
had arisen by the modification of pre- 
existing forms, and he further ad- 
vanced an hypothesis as to the way 
in which this change had come about. 


WHAT EVOLUTION IS 15 


His views were ably seconded by a 
number of the most distinguished 
savants of his time, among whom 
may be numbered the great Goethe. 
Of Lamarck’s confréres Geoffroy 
Saint-Hilaire took up the subject in 
public discussion with Cuvier, per- 
haps the greatest naturalist of his 
day. Cuvier, whose opinions were 
anti-evolutionary, resisted with all his 
strength and authority the rising tide 
of new opinion and succeeded in 
checking its flow, for it was generally 
concluded at the end of the contest 
that descent with modification must 
be permanently abandoned. 

For some decades the storm sub- 
sided, for the appearance of the little 
volume entitled “ Vestiges of the Nat- 
ural History of Creation,” published 
by Robert Chambers in 1844, was 
only a ripple on the surface. Then 
in 1859, with the publication of Dar- 


16 WHAT EVOLUTION IS 


win’s “Origin of Species,” the storm 
broke afresh, this time not to be 
turned aside till it had swept the 
shores clear of the wreckage of old 
ideas. 

Everyone knows the great public 
upheaval that followed the appearance 
of the “Origin of Species.” The 
scientific world had been prepared for 
it by a paper on the theory of natural 
selection, published by Darwin and 
Wallace in the preceding year; but 
considering the long period of rela- 
tive quiescence that had preceded 
1859, even scientists must have been 
startled at the uproar that broke 
forth. Darwin and his able coadju- 
tor, Huxley, had the double task of 
showing to the world that, in contrast 
with special creation, descent with 
modification had taken place, and that 
natural selection was the driving 
force behind this process. In the 


WHAT EVOLUTION IS 17 


days of Lamarck the chief question 
was on the modifiability of species, 
and on this first line of attack the 
forces of evolution received for the 
time being a serious setback. But 
under Darwin and Huxley a new of- 
fensive was launched, and after a 
vigorous campaign both objectives 
were attained. It is to the credit of 
Charles Darwin, and his body of able 
supporters, that the scientific world 
was finally brought to accept the prin- 
ciple of descent with modification, 
and natural selection as the means 
whereby it was accomplished. 

The evidence that convinced the 
world in Darwin’s day that descent 
with modification, and not special 
creation, was the means of peopling 
the present globe with its variety of 
living forms was meager in the ex- 
treme as compared with what might 
be drawn upon to-day, but it never- 


18 WHAT EVOLUTION IS 


theless covered the ground and may 
be profitably looked into now, since 
it still affords the real support on 
which the doctrine of evolution rests. 
This body of evidence comes from five 
important fields in biology: compara- 
tive anatomy, embryology, the study 
of fossils, zoogeography, and the 
nature of rudimentary organs. 


Ill 
EVIDENCE ON EVOLUTION 





EVIDENCE ON EVOLUTION 


1. FROM COMPARATIVE 
ANATOMY 


AN important body of evidence that 
bears on the evolutionary problem 
comes from the field of comparative 
anatomy. A little over a century ago 
the school of comparative anatomy 
was founded by Cuvier (1769-1832), 
who, though an _ anti-evolutionist, 
showed that animals in their structure 
were not immensely diverse, but con- 
formed to general plans or types of 
organization. From this standpoint 
each animal could be said to represent 
its type, subject to such modifications 
as its special mode of life called for. 
Thus under the enormous diversity 
of animal forms there was in reality 
a more or less hidden uniformity. 
This principle of type organization 


22 WHAT EVOLUTION IS 


is abundantly illustrated by many 
sets of organs. For instance, the 
human arm is composed of parts that 
recur in the corresponding organs in 
other animals. The arm of man, as 
shown on page 23, contains four sets 
of bones: the single bone of the upper 
arm, the pair of bones in the forearm, 
the group of small wrist bones, and 
the series of elongated bones in the 
five digits. All these groups of bones 
recur with great regularity in the 
foreleg of the cat, of the turtle, and 
of even so lowly organized an animal 
as the frog. The wing of a bat, when 
it is examined, is found not to be con- 
structed upon a plan peculiar to itself, 
but to be a modification of the type of 
structure already described for man, 
in that the single bone of the upper 
arm is present, as are the pair of 
forearm bones, the wrist bones, and, 
enormously elongated to carry the 








WHAT EVOLUTION IS 25 


web of the wing, the finger bones. In 
the bird, unlike the bat, the expansion 
of the wing is due to feathers but the 
skeletal axis that supports the feath- 
ers 1s formed from a set of bones 
such as occur in the human arm, ex- 
cept that the fingers are reduced in 
number and bound together to serve 
as a supporting axis for the larger 
plumes. The flipper of a whale or 
of a porpoise, superficially so unlike 
the human arm, nevertheless shows 
closely compacted within it the bone 
of the upper arm, the two forearm 
bones, wrist bones, and finger bones. 
In the foreleg of the horse the bone 
corresponding to that in the upper 
arm of man is hidden in the flesh of 
the animal. This bone is followed, 
however, by the two bones of the 
forearm, fused together, by the wrist 
bones, which are situated at what is 
popularly called the knee of the horse, 


26 WHAT EVOLUTION IS 


and by a row of bones which repre- 
sent the middle finger of man. These 
bones in man are four in number, 
counting the deep-seated long bone 
in the palm, and this number is ex- 
actly reproduced in the horse, in which 
the last member of the series carries 
the hoof corresponding to the human 
nail. The front leg of the horse not 
only rests on what is equivalent to 
the enormously enlarged middle fin- 
ger of man, but it contains, on either 
side of this digit, relatively inconspic- 
uous splint bones which represent our 
index and our ring fingers. 

By the comparative method it is 
thus possible to demonstrate that 
such apparently diverse organs as the 
arm of a man, the wing of a bat, and 
the foreleg of a horse are similarly | 
organized and are merely modifica- . 
tions of one type of structure. 

Animals and plants abound on 


WHAT EVOLUTION IS 27 


every hand with series of parts in 
which the elements are related, as in 
the examples just described, and it is 
one of the achievements of the com- 
parative method that it has thus 
yielded incomparably rich and signifi- 
cant material for philosophical bi- 
ology. By its means anatomy has 
been lifted from a discipline of dead 
description to a science rich in prob- 
lems and resources. 

This advance in method had an 
immediate and decisive bearing on 
the evolutionary question. If organ- 
isms were separately created there 
would be every reason to expect that 
they would be constructed upon indi- 
vidual plans, and not the least ground 
to anticipate in them an underlying 
common type of structure. If, how- 
ever, they have evolved from a 
common ancestry, precisely such un- 
derlying similarities might be ex- 


28 WHAT EVOLUTION IS 


pected. The human arm, the foreleg 
of a quadruped, the wing ofa bird, and 
the flipper of a whale have a common 
plan of organization because these 
animals have had a common ancestry. 
Thus the science of comparative an- 
atomy yields results that support 
most completely the evolutionary 
idea, and that give no ground for the 
assumption of special creation. It is 
a remarkable fact that Cuvier, who, 
as already observed, was a strong 
anti-evolutionist, should have been 
instrumental in founding and in 
partly developing a school that in the 
end yielded such important evidence 
in favor of descent with modification. 


WHAT EVOLUTION IS 29 


2. FROM EMBRYOLOGY 


THE science of embryology deals 
with the growth of animals from the 
ege to the adult, and this science, 
though of comparatively recent ori- 
gin, has had an important bearing on 
evolutionary problems. It is a com- 
monplace that, in the development of 
any animal, the creature does not 
start life as a miniature of what it is 
finally to be and then slowly enlarge 
until it reaches adult proportions, but 
it begins life in a state very unlike its 
adult condition and only gradually 
assumes an outline that is associated 
with its final form going through a 
series of changes, often very pro- 
found, till it finally arrives at its ma- 
ture state. 

Most common animals afford ex- 
amples of this kind of growth. 


30 WHAT EVOLUTION IS 


Frogs, for instance, lay eggs and 
from these are hatched, not frogs, 
but tadpoles which eventually, through 
a series of rather complicated bodily 
changes, reach the condition of an 
adult frog. 

The remarkable peculiarity of this 
kind of growth is that, during the 
steps in its progress, the young ani- 
mal often shows striking resem- 
blances to other animals. Thus, in 
the instance just given, the tadpole of 
the frog has unquestionably fish-like 
characteristics. Instead of having 
front and hind legs for locomotion as 
in the adult frog, the tadpole moves 
about by means of a flattened tail in 
a way similar to that of a fish. More- 
over, the tadpole has in its neck a 
system of gills by which it breathes 
precisely as a fish does. As develop- 
ment goes on, these gills are gradu- 
ally absorbed and are replaced by 


WHAT EVOLUTION IS 31 


lungs when the tadpole approximates 
the state of the frog. But before this 
metamorphosis has taken place the 
tadpole, in structure and in activities, 
recalls in many important particulars 
the state of a fish. 
Examples of this kind may also be 
found in the course of human develop- 
ment. When the human embryo is a 
small fraction of an inch in length a 
definite number of narrow transverse 
clefts appear on its neck as shown 
in the uppermost figure on page 33. 
These clefts lead into the throat and 
correspond in position to the gill open- 
ings of fishes. Moreover the sup- 
ports between the clefts, the arches, 
which are numbered in the figure, 
carry large arteries resulting from 
the division of the main blood-vessel 
that emerges from the embryonic 
heart, just as the gill arches of fishes 
are supplied by large vessels from the 


32 WHAT EVOLUTION IS 


heart of the fish. These embryonic 
organs in man never serve for breath- 
ing as the corresponding parts do in 
fishes, but in gross structure the 
human gill arches recall in a most 
striking way the gill system of fishes. 
As the development of the human 
embryo proceeds, the gill clefts are 
obliterated, excepting the first one 
which is retained in forming the aper- 
ture of the external ear. 

Thus the frog and man and in fact 
all the higher vertebrates show in a 
temporary way gill clefts and gill 
arches, both of which are the perma- 
nent possessions of the fishes. 

That higher animals should, in the 
course of their individual develop- 
ment, exhibit temporarily features 
that are permanent in lower animals, 
seems to be a rule of organic growth. 
It certainly is abundantly exempli- 
fied in many forms. Thus in all 


WHAT EVOLUTION IS 33 





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' WHAT EVOLUTION IS 35 


true backboned animals a notochord, 
or supporting rod, precedes in devel- 
opment the real backbone of these 
forms and is replaced by this bone, 
except in the very lowest fishes where 
the notocord is the permanent and 
only organ of support. Another ex- 
ample may be found in the embryonic 
human being where small ribs occur 
attached to the neck vertebrae. As 
development advances these ribs fuse 
with the vertebrae and are thus lost 
to view, but in lower animals, like the 
alligator, neck or cervical ribs are 
persistent throughout life. Again 
all animals that reproduce sexually 
pass through an egg stage in which 
they are, for the time being, a single 
cell. This state is a permanent condi- 
tion in the simplest animals, the pro- 
tozoans, which are very usually only 
single cells. Innumerable examples 
such as these might easily be given. 


36 WHAT EVOLUTION IS 


The peculiarity of development, 
that higher animals pass in a tempo- 
rary way through stages that are per- 
manent in lower forms, has long been 
recognized as a characteristic feature 
of general growth. It has sometimes 
been dignified as a law of develop- 
ment and has been designated, in 
honor of the father of modern em- 
bryology, von Baer’s law. As such it 
was strongly advocated by Louis 
Agassiz. In a more descriptive way 
it has been spoken of as the law of 
recapitulation, for the reason that 
such features in the development of 
an animal as those already alluded to 
recapitulate, in a rough way, the ra- 
cial history of the animal concerned. 
Thus the presence of gill slits in the 
embryo of the human being indicates 
that a gill-breathing animal is to be 
included in our remote ancestry. As 
Huxley facetiously remarked in dis- 


WHAT EVOLUTION IS 37 


cussing this question years ago, each 
animal in its development climbs its 
own ancestral tree. 

The facts associated with the law 
of recapitulation are quite meaning- 
less from the standpoint of special 
creation, but from that of descent 
with modification they receive a simple 
and adequate interpretation. A de- 
veloping animal shows temporary re- 
semblances to lower forms, because 
these forms represent steps in its 
own racial history. 


38 WHAT EVOLUTION IS 


3. FROM GEOLOGY 


THE evidence on the evolutionary 
problem to be drawn from geology 
turns largely on the question of fos- 
sils. A fossil is anything dug from 
the earth. Specifically fossils are 
bones, shells, or even delicate struc- 
tures such as ferns and the like, that 
have been more or less converted into 
stone and have been exhumed from 
their hiding places in the rocks. 

The ancients were acquainted with 
fossils, but they regarded them in a 
light very different from that in 
which the modern naturalist looks 
upon them. Fossils were believed by 
the ancients to have had something 
to do with nature’s formative proc- 
esses. These early observers were, 
for the most part, believers in spon- 
taneous generation. They accepted 


WHAT EVOLUTION IS 39 


the view that new organisms, plants 
and animals, were being continually 
produced by nature, that fish, frogs, 
worms, and the like were being 
formed continually from the mud 
and slime in the bottoms of ponds, 
that maggots were being generated 
spontaneously in decomposing meat, 
and that parasitic worms were being 
produced in the interior-of the ani- 
mals whose bodies they inhabit; in 
short that the process of spontaneous 
generation pervaded nature gener- 
ally. They were not conversant with 
the modern idea, arrived at after 
long experimentation, that all living 
things come from preéxisting living 
things and that none are formed de 
novo. ‘Vhey held that mother earth 
was continually producing new life 
from her own substance. 

With this doctrine in mind, their 
interpretation of fossils was very 


40 WHAT EVOLUTION IS 


different from that given by the mod- 
ern naturalist. When they discov- 
ered the impressions of shells in the 
rocks of the mountainside they recog- 
nized at once the inappropriateness 
of the situation, and they believed 
that they had before them evidence 
of nature’s unsuccessful effort to 
produce new life. She, in her prod- 
igality of productiveness, had started 
the formation of an aquatic animal 
on a mountainside and, in conse- 
quence of the unfavorableness of 
the site, the process had failed of 
completion and a mere trace of its 
beginning was thus left stranded in 
inhospitable surroundings. 

This general view of the nature of 
fossils was current for many gener- 
ations, but as early as the fifteenth 
century, Leonardo da Vinci (1452- 
I519) recognized that shore lines 
shifted, that the earth’s crust was ele- 


WHAT EVOLUTION IS 41 


vated and depressed, and that what 
was once sea bottom, with its myriads 
of marine plants and animals, might 
well become mountainside with its 
contained fossils. Gradually the 
opinion grew that all fossils were the 
remains of once living organisms, 
and this doctrine, advanced through 
the efforts of such workers as Fra- 
castoro, Steno, Hooke, and others, 
had gained complete acceptance in 
the days when Lamarck( 1744-1829) 
and Cuvier (1769-1832) were found- 
ing modern paleontology. 

Concurrent with the growth of the 
new ideas about fossils came the con- 
ceptions of stratigraphic geology. 
Rocks not only contain the fossil re- 
mains of once living organisms, but 
the underlying rocks hold remains of 
an older date than do those above 
them. Such a sequence of fossils, as 
is implied by this view, was advocated 


42 WHAT EVOLUTION IS 


by Woodward (1665-1728), Valis- 
nieri (1661-1730), Smith (1769- 
1829), and especially by Cuvier 
(1769-1832). Cuvier further rec- 
ognized that the older rocks con- 
tained fossils of a simpler type than 
the more recent ones did, and he ex- 
plained this difference by assuming 
that periods of cataclysmic destruc- 
tion alternated with periods of special 
creation. This doctrine was carried 
to an extreme by d’Orbigny (1802- 
1857) who claimed for the past some 
twenty-seven such alternations. But 
the idea of cataclysmic alternations 
was defeated by the school of uni- 
formitarians, whose advocates, like 
Lyell (1797-1875 ), saw in the present 
forces of nature an explanation of 
the past and supported the idea of 
continuity, not interruption, in the 
organic series. By these steps the 
modern conception of fossils and 


WHAT EVOLUTION IS 43 


their significance was reached; they 
are the remains of once living organ- 
isms,and they discloseacontinuousand 
real history of plant and animal life. 
When this history is looked into, 
it is found to have, as might be ex- 
pected, a profound bearing on evolu- 
tionary matters. It is by no means 
easy to determine how long living 
things have existed on the earth. 
Estimates vary from a hundred-mil- 
lion to two thousand-million years. 
But from an evolutionary standpoint 
such enormous periods, and even 
such differences in the estimates, are 
not so significant as the kinds of or- 
ganisms that are shown to be present 
at different periods in the earth’s 
history and the sequences that this 
history discloses. Sketched very 
broadly, it may be said that during 
about the first two-thirds of the period 
in which life has been on the globe 


44 WHAT EVOLUTION IS 


only invertebrates were present. 
These include sponges, corals, star- 
fish, worms, crustaceans, insects, 
brachiopods, snails, clams, and other 
shellfish. Vertebrates, or backboned 
animals, first arose about the begin- 
ning of the last third of the period 
of life on the globe, and the earliest 
fossil representatives of this group 
were the fishes. These were followed, 
near the opening of the last quarter, by 
the amphibians which were succeeded 
by the reptiles, the mammals, and the 
birds in the order named. Man has 
been present on the globe during some- 
what less than the last hundredth of 
the total period of living things. 
When this sequence is reviewed it 
is seen at once to present a reasonable 
plan. Invertebrates precede verte- 
brates, fishes antedate amphibians 
and these in turn come before reptiles, 
mammals, and birds. Man appears 


WHAT EVOLUTION IS 45 


only near the very end, long after the 
group of which he is a member, the 
mammals, had established itself. 

The sequence of forms that is here 
portrayed is an orderly one and the 
order is such as would be expected on 
evolutionary grounds. Had special 
creation been the rule of nature there 
would have been no reason for inver- 
tebrates to have preceded vertebrates 
in their time of appearance, or for 
fishes to have come before amphibians 
and the like. But this order of ap- 
pearance being such as it is, one must 
conclude that this aspect of the fossil 
series gives unequivocal support to 
the evolutionary view. 

Facts of the kind that have just 
been narrated were well known in 
Darwin’s day. Since that time the 
study of fossils, and particularly of 
vertebrate fossils, has enormously 
expanded. Huxley in his time was 


46 WHAT EVOLUTION IS 


much interested in the fossil series 
illustrating the evolution of the horse. 
As is well known, this animal can be 
shown to have descended from a small 
multi-toed creature of the approxi- 
mate size of a fox. In the early days 
of the evolutionary controversy this 
was the one series of developing forms 
that the paleontologist could point to 
with assurance. To-day scores of 
such series are known not only in the 
vertebrates but in the invertebrates. 
Even with man the call for the miss- 
ing link seems to have subsided, for the 
sequence in so many of the fossil series 
is so nearly complete that it seems to 
be only a matter of diligence and time 
till the fossil record of any important 
line can be brought to light. The imper- 
fections inthe fossil seriesareno longer 
interpreted as real and significant 
breaks but as interruptions sooner or 
later to be filled as science advances. 


WHAT EVOLUTION IS 47 


4. FROM ZOOGEOGRAPHY 


THE past and present distribution of 
animals on the surface of the globe 
has important bearings on the evolu- 
tionary problem. Animals are not 
scattered in a haphazard fashion over 
the earth, but show a marked regular- 
ity in their occurrence. This can be 
well illustrated by what is known of 
the mammals. The group of mam- 
mals is made up chiefly of the common 
beasts of the field and forest, but it 
includes also such exceptional forms 
as the bats, among aérial creatures, 
and the whales and porpoises of the 
sea. Mammals have warm blood, 
they produce milk with which they 
nourish their young, and they are pro- 
vided with more or less hair. 

Almost all the mammals bring forth 
their young in a highly developed, 


48 WHAT EVOLUTION IS 


active state. Two of them, however, 
the Australian porcupine and the 
duckbill, lay eggs. These two mam- 
mals, in addition to the habit of 
laying eggs, have many primitive char- 
acteristics. They constitute the low- 
est group of this class of animals. 
They are commonly designated as 
monotremes. The remarkable feature 
about them, from the standpoint of 
the present discussion, is that they are 
not found broadcast over the earth 
but are limited to a very distinct zoo- 
geographical area, the Australian 
region. Thus the total representation 
of this striking group of forms is re- 
stricted to a small part of the globe. 
The Australian region is not only 
the habitation of the monotremes; it 
is also the home of the marsupials. 
These are mammals, such as the pha- 
langers, the wombats, and the kan- 
garoos, the females of which are 


WHAT EVOLUTION IS 49 


commonly characterized by the pres- 
ence of a pouch on the abdomen. This 
pouch, which contains the milk glands, 
serves as a receptacle for the young 
after their birth. Most persons have 
seen in our zoological gardens the 
female kangaroo with her offspring 
and have noticed how the young, when 
alarmed, run to the pouch, enter it, 
and are carried off by the mother. 
The marsupials, like the monotremes, 
are very primitive mammals. Ex- 
cepting the American opossums and 
one other pouched mammal in South 
America, all marsupials are limited 
to the Australian region. No mar- 
supial occurs in Eur-Asia or in Africa. 
Thus the marsupials, like the mono- 
tremes, illustrate a common peculiar- 
ity of animal distribution, namely, that 
many large and important groups are 
limited to well circumscribed and often 
relatively small areas of the earth. 


so WHAT EVOLUTION IS 


This topic is still better illustrated 
if we take into consideration the 
distribution of fossil, as well as of 
living forms. Again the mammals 
may serve as illustrations. Sloths and 
armadillos constitute a group of mam- 
mals very striking in their distribu- 
tion. 

The modern sloths are arboreal 
creatures of moderate size; they feed 
upon the succulent stems and leaves 
of tropical trees. By means of their 
curved claws, they hook themselves 
through the tangle of branches in the 
forest jungle. They are almost in- 
capable of locomotion on the ground 
and when by accident they fall, they 
move about in a most awkward fash- 
ion in regaining their haunts. 

The modern armadillo is a burrow- 
ing animal chiefly active at night. Its 
covering of segmented shelly pieces 
gives it more the appearance of a 


WHAT EVOLUTION IS 51 


reptile than of a mammal, but its 
warm blood, its mammary glands, and 
the hair that projects outward be- 
tween the segments of its shell pro- 
claim it a true mammal. 

Modern sloths and armadillos are 
limited to the new world particularly 
to South and Central America though 
the armadillos extend northward 
through Mexico into the southern 
borders of the United States. None 
of these forms occur in the old world 
or in fact elsewhere than in the region 
just described. 

Fossil sloths and armadillos are 
known in considerable numbers. Some 
of these are of huge size. Fossil 
eround sloths have been discovered 
whose skeletons justify the belief that 
the living animal must have been as 
large as a rhinoceros. Armadillo- 
like animals, the glyptodons, have been 
found whose skeletons are almost as 


32. WHAT EVOLUTION IS 


large as those of oxen. The fossil re- 
mains of all these sloths and armadil- 
los are found exclusively in the new 
world and in that part south of the 
central United States. It is a remark- 
able fact that, notwithstanding the 
great difference between these fossil 
sloths and armadillos and their mod- 
ern representatives, the living and the 
fossil forms should agree almost 
exactly in the regions where they 
occur. One is forced to conclude from 
facts of this kind, as well as from the 
circumstance, that most well-defined 
groups of modern animals, like the 
monotremes and the marsupials, oc- 
cupy definitely restricted areas, that 
members of the same great group have 
had a common origin, for had they 
been specially created their distribu- 
tion on the earth’s surface would have 
called for no particular regularity. 


WHAT EVOLUTION IS _ 53 


5. FROM RUDIMENTARY 
ORGANS 


THE last biological topic to be con- 
sidered in the present account as bear- 
ing on the problem of evolution has 
to do with rudimentary organs. Rudi- 
mentary organs are those organs that 
are without use or function. They 
are like the buttons on the sleeve of a 
man’s coat; they are essentially use- 
less and sometimes worse than useless. 
A well-known rudimentary organ, 
from the human body, is the vermi- 
form appendix of the large intestine. 
This organ is a blind tube several 
inches in length and attached to the 
large intestine near its beginning. It 
is shown to the right in the figure on 
page 55. It is easily subject to in- 
flammation and forms a danger center 
in the intestinal tract. In diseased 
* states it is regularly removed by the 


54 WHAT EVOLUTION IS 


surgeon and even in normal condi- 
tions it is frequently excised as a pre- 
cautionary measure. No one is known 
to suffer any inconvenience from its 
loss; in fact a person is commonly re- 
garded as better off without it than 
with it. In consequence of its com- 
plete lack of function, it is a thor- 
oughly good example of a rudimentary 
organ. 

The condition of the vermiform 
appendix in man is by no means 
typical of this organ in other mam- 
mals. Cats show no sign of it, but in 
rabbits it is a highly developed struc- 
ture and is intimately concerned in this 
animal with the regular activities of 
the large intestine. 

Other rudimentary organs in man 
are easily pointed out. The external 
ear of the human being has attached 
to it three thin muscles, one above the 
ear, a second behind that organ, and a 


WHAT EVOLUTION IS 55 


Cat 


Rabbit 





WHAT EVOLUTION IS 57 


third in front of it. Most persons 
have no power of motion in these 
muscles and, in such instances, the 
muscles may be looked upon as purely 
rudimentary, but occasionally an in- 
dividual will be found who can con- 
trol them to a slight degree and who 
can thereby move his external ear. 
Even in such instances, however, the 
amount of motion is extremely slight 
compared with that seen in such 
animals as the horse and the dog, 
where the tube of the outer ear is 
directed with great freedom in a 
variety of ways and is used asa means 
of discovering the direction of sound. 
From the standpoint of actual useful- 
ness, the three muscles attached to the 
human ear are quite as rudimentary 
as is the human vermiform appendix. 

Well within the angle of the human 
eye next the nose is a slight fold of 
whitish membrane, the so-called plica 


58 WHAT EVOLUTION IS 


semilunaris. No use is known for this 
organ in man but in the cat, as one can 
readily see by direct inspection, in 
place of this fold there is a nictitating 
membrane, or third eyelid, which by 
its free movement back and forth 
across the eyeball serves as a means 
of protecting and cleansing that or- 
gan. The plica semilunaris in man 
is a completely useless remnant of this 
third eyelid. 

In an enumeration of the rudimen- 
tary organs in man made some years 
ago by Wiedersheim approximately 
ninety such parts were noted. This 
seems like a considerable list for one 
species, but it is probably by no means 
exhaustive. Most higher animals, like 
man, abound in a great variety of such 
useless parts. 

From the standpoint of special 
creation, it is by no means easy to 
explain the presence of such function- 


WHAT EVOLUTION IS 59 


less organs. If animals were spe- 
cially created why should they contain 
scores of parts that are without use 
and that in some instances, like the 
vermiform appendix, are positively 
deleterious? A satisfactory answer 
to this question has never been given. 
From the standpoint of evolution, 
however, rudimentary organs are 
structures in process of disappear- 
ance, organs that are just dropping 
below the horizon of serviceableness. 
Their presence in a given form in- 
dicates that they were: functional in 
some ancestor of that form, and that 
as evolution proceeded and the species 
changed, it dropped this particular 
part from the level of functional sig- 
nificance to that of uselessness. Such 
an explanation of the presence of these 
organs accords completely with what 
is known of them from all points of 
view. 


60 WHAT EVOLUTION IS 


6. CONCLUSION 


WE have now completed a brief sur- 
vey of some of the more important 
fields of evidence concerning descent 
with modification. We have examined 
this question in the light of compara- 
tive anatomy, of embryology, of geol- 
ogy, of zoogeography, and of the study 
of rudimentary organs. In none of 
these aspects of the problem has there 
appeared reason for assuming that 
special creation has been the method 
by which the diversity of plants and 
of animals at present on the globe has 
been produced and in all of them there 
has been shown either strong evidence 
in favor of descent with modification 
or a state of affairs open to ready in- 
terpretation from this standpoint. 
The several lines of evidence that 
have been considered in this connec- 


WHAT EVOLUTION IS 61 


tion could scarcely be said to have 
been available in the time of Lamarck, 
for most of them have been the result 
of the scientific endeavor of the last 
hundred years. It is therefore not 
surprising that in his day evolution 
received a serious setback, for at that 
time not enough was known to give 
the question a fair hearing. 

Even when Darwin wrote, knowl- 
edge on many important points was 
very incomplete compared with what 
it is to-day. It is, however, a sig- 
nificant fact that practically all the 
lines of evidence cited by Darwin as 
confirmatory of evolution are signifi- 
cant to-day and much more exten- 
sively supported than they were in his 
time. The confirmation thus received 
is the result of the discovery and im- 
partial accumulation of new facts on 
lines that bear on the question at hand. 
If to the naturalist of Darwin’s time 


62 WHAT EVOLUTION IS 


the evidence in favor of evolution 
seemed persuasive, that which can be 
brought forward now would have been 
overpowering. It is this strength of 
the modern position that has placed 
every biologist of any standing what- 
soever on the side of evolution. In 
other words, practically all biologists 
to-day accept without any reserva- — 
tions descent with modification as a 
process of nature. They no longer 
question this view. This statement 
cannot be emphasized too strongly. 
At the same time that these biolo- 
gists accept descent with modification 
as anactual occurrence in nature, they 
are most skeptical and reserved about 
what may be called the driving force 
behind descent. What is there in 
nature that has kept in motion this 
incredible capacity to produce new 
species? How is it that from age to 
age large and ever larger floods of 


WHAT EVOLUTION IS 63 


new forms have burst forth? To this 
question no biologist has a clear and 
unequivocal answer. It is this uncer- 
tainty that has been seized upon by a 
few thoughtless critics who have at- 
tempted to discredit in the eyes of the 
general public the well established fact 
of descent with modification by con- 
fusing it with the explanations of de- 
scent. This confusion, commonly due 
to ignorance, is the source of most of 
the contentions now met with in evo- 
lutionary controversies. It does not 
characterize the clear thinker. Be- 
cause biologists have not as yet dis- 
covered how evolution takes place is 
no reason for denying evolution itself. 

The explanations of the evolution- 
ary process thus far offered are large 
in number. They include, to mention 
only some of the most important, 
Lamarck’s hypothesis, Darwin’s nat- 
ural selection, Naegeli’s idioplasmic 


64 WHAT EVOLUTION IS 


hypothesis, Eimer’s orthogenesis, De 
Vries’s mutation theory and the like. 
In so brief a survey as this volume 
offers it will be profitable to consider 
only the more noteworthy of these 
views and in conformity with this plan 
the next chapter will contain brief 
critical accounts of Lamarck’s hypoth- 
esis, of Darwinism or the theory of 
natural selection, and of the mutation 
theory of De Vries. 


OL, 
FACTORS IN EVOLUTION 








ae 


i 


i < " " av? As 
dia eA ek 
Pra aa’ | aT) Per hd 
ae ee. WO CY ee 





tn 


FACTORS IN EVOLUTION 
PAPER EPEAT ORY 


In the early discussions on evolution 
it soon became apparent that, com- 
pared with the biblical account of 
creation, descent with modification re- 
quired a relatively enormous length 
of time. This contrast between the 
two views was used by Cuvier in his 
opposition to Lamarck. Cuvier had 
careful measurements made of the 
skeletons of mummified Egyptian 
animals and of their recent represen- 
tatives. No significant differences 
could be detected on comparing these 
two sets of measurements and Cuvier, 
therefore, concluded that if no meas- 
ureable changes had overtaken ani- 
mals in the three thousand years that 
separated the mummified from the 
modern forms, it was useless to con- 


68 WHAT EVOLUTION IS 


sider the possibilities of a process 
which, if it occurred at all, was almost 
inconceivably slow. Although Cuvier 
has since been shown to be wrong in 
his general deductions, the results of 
such speculations as this led trans- 
_ formists in the early days to assume a 
very long period for the evolution of 
life on the earth, a conception quite in 
line with the growing uniformitarian 
geology of the day. The assumption 
of a relatively great age for the earth 
and its inhabitants has been entirely 
justified by subsequent scientific in- 
quiry, but in the days of Cuvier and 
Lamarck and even in the time of Dar- 
win it was based on much less con- 
vincing evidence than at present. 
To-day it is beyond dispute that the 
age of the earth as the abode of life is 
to be reckoned in hundreds if not 
thousands of millions of years. 

In consequence of these growing 


WHAT EVOLUTION IS 69 


opinions, there arose a belief among 
naturalists of the transformist school 
that evolution was so slow and grad- 
ual a process that no direct observa- 
tion of it could ever be made. The 
life of man was not long enough to 
admit of even a glimpse at evolution- 
ary change. This view was current 
in Darwin’s day and prevailed more 
or less to the end of the nineteenth 
century. It served as a most unfor- 
tunate deterrent to scientific research, 
for it discouraged investigators from 
attempting any direct study of a proc- 
ess whose operations seemed to be so 
infinitely slow. 

With the advent of the twentieth 
century a new phase in evolutionary 
investigation appeared. Through the 
work of Tschermak, of Correns, and 
particularly of De Vries the subject 
passed from the observational and 
speculative stage to the experimental 


70 WHAT EVOLUTION IS 


one, and instead of looking upon evo- 
lution as a process so slow as to be 
imperceptible, it was soon believed, as 
a result of experimental test, to be 
relatively rapid at least in particular 
instances. In fact it was declared 
that species might be created almost 
over night. Such a radical change of 
view had a profound effect on the 
growth of the subject and though the 
new programme may not have real- 
ized all that was expected of it, it 
brought the science into a vastly more 
wholesome state and led to positive 
growth of a most encouraging kind. 
In this revival of activity all the 
older explanations of evolution were 
brought to the test with the result that 
such ideas as Eimer’s orthogenesis, 
in which variation was supposed to 
occur in definite and predetermined 
directions, and Naegeli’s idioplasm 
theory, in which an internal perfect- 


WHAT EVOLUTION IS 71 


ing principle was assumed, lost ground 
and the field was left almost ex- 
clusively to Lamarckism, Darwinism 
and the mutation theory. A consid- 
eration of these views will now follow. 


} 


72 WHAT EVOLUTION IS 


2, LAMARCKISM 


LAMARCK’S hypothesis as to the means 
by which evolution has been accom- 
plished is best stated in his “ Philos- 
ophie Zoologique”’ published in 1809, 
a year which is noteworthy as the 
birth year of Charles Darwin. La- 
marck’s explanatory views excited 
very little attention at the time of their 
publication, for, so far as the scientific 
world took any interest in evolution 
at all, it was concerned with the ques- 
tion of the validity of this doctrine 
rather than withits explanation. Fifty 
years later when Darwin advanced 
natural selection the explanatory as- 
pects of this question came much more 
to the front. Then a contrast be- 
tween Darwin’s views and Lamarck’s 
views could be drawn. 


WHAT EVOLCUTIONZ IS 73 


The explanation offered by La- 
marck turned chiefly on the effect 
upon organisms of the surroundings 
or environment. Lamarck noted that 
marsh plants, such as the aquatic 
Ranunculus, which grew partly sub- 
merged and partly out of water, had 
leaves of different shapes in the two 
situations. Under water the leaves 
were finely divided, but in the air they 
were simply lobed. This difference 
he rightly conceived to be due to the 
environment, one situation producing 
the first type of leaf and the other the 
second. He looked upon this as a 
direct effect of the surroundings and 
regarded it of great importance par- 
ticularly with plants. A special plant 
being thus directly dependent upon its 
surroundings for its peculiar form, any 
change in these surroundings would 
be likely to be followed by a change 
in the form of the plant, that is, an- 


74 WHAT EVOLUTION IS 


other form would arise and evolution 
could be said to have taken place. 

Lamarck conceived the effect of en- 
vironmental change on animals to be 
carried out in a rather more complex 
way than on plants. He illustrated 
this by several examples such as the 
webbed foot of water birds and the 
long neck of the giraffe. 

Lamarck rightly believed that land 
birds were the ancestors of water 
birds, and in thinking of the transi- 
tion, he pictured land birds coming 
more and more to frequent the shore, 
to pass much of their time in shallow 
water and to seek their food there. 
Such newcomers would from time to 
time get into deep water and naturally 
attempt to propel themselves by kick- 
ing with their legs. The muscular 
exercise of kicking would induce an 
extra flow of blood to the legs whose 
bones, muscles, skin, and the like 


WHAT EVOLUTION IS 7s 


would respond by extra growth. In 
this way the skin between the toes 
would become firmer, tougher, and 
more extensively developed. These 
effects would be increased in the de- 
scendent stock, and as they accu- 
mulated generation after generation, 
the passage would be accomplished 
from the webless foot of the land 
bird to the webbed foot of the water 
bird. 

Lamarck conceived that the gi- 
raffe’s neck, to take another of his 
examples, was lengthened by a similar 
process. These animals were sup- 
posed to browse among the branches 
of trees. In their endeavors to reach 
the leafy food, they would naturally 
exert the muscles of the neck and this 
activity would induce an extra flow of 
blood to that region. In consequence 
the muscles, bones, and other parts of 
the neck would increase in size, just 


76 WHAT EVOLUTION IS 


as the arm of a man increases under 
exercise. Asa result of this activity 
continued through generation after 
generation, the neck of the giraffe 
would lengthen and eventually reach 
the extreme condition seen to-day. 
Both these instances involve a proc- 
ess more complex than that in the 
partly submerged plant, but in both 
of them the environment is the fun- 
damental factor. With the bird the 
change from inland surroundings to 
a shore environment is the important 
element, and with the giraffe the 
change from a region where browsing 
was low to one where it was among 
trees. Thus as with the plant, en- 
vironmental differences play the chief 
part in the evolution of these animals. 
Put briefly, the Lamarckian scheme, 
as applied to animals, is as follows: 
a change in the environment is fol- 
lowed by a change in habit, and a 


WHAT EVOLUTION IS 77 


change in habit is followed by a 
change in structure. Thus the condi- 
tion of the animal is modified and 
evolution is the result. 

Such an application of the La- 
marckian principle, as is involved in 
the last two examples, requires what 
may be called the indirect influence of 
the environment in contrast with the 
direct influence as seen in most plants, 
but in both direct and indirect influ- 
ences, the environment and its changes 
are the paramount elements. 

In addition to the general principle 
that has just been illustrated, La- 
marck also called attention to certain 
subordinate principles that he believed 
to be significant in evolution. First 
of these was the principle of use and 
disuse. Organs that are exercised 
tend to increase in size, and organs 
that are not exercised tend to shrink. 
This is so obvious a matter in every- 


78 WHAT EVOLUTION IS 


day life that it needs no special illus- 
tration and no one denies it. 

Another principle that Lamarck 
advanced was the principle of effort, 
that in order to accomplish an end an 
animal must make an effort, must 
exert itself. If it did not so do its 
effective powers would diminish. This 
is an element of a psychological na- 
ture; it has a certain vague and in- 
tangible side not involved in the 
principle of use and disuse, for in- 
stance. It nevertheless plays no un- 
important part in Lamarck’s general 
hypothesis. 

The scheme advanced by Lamarck, 
and briefly outlined in the preceding 
paragraphs, carries with it the im- 
pression of great naturalness. Every- 
one knows that activity or lack of 
activity modifies an organ and, grant- 
ing that the changes thus produced 
are handed on generation after gen- 


WHAT EVOLUTION IS 79 


eration and emphasized, evolution 
seems to be a natural consequence. Is 
not this precisely the method by which 
plants and animals are moulded to 
their surroundings; is not this, in 
other words, the driving force that 
lies behind evolution? On the surface 
it seems as though Lamarck’s hy- 
pothesis must indeed offer the true 
explanation. 


80 WHAT EVOLUTION IS 


3. LAMARCKISM CRITICIZED 


NOTWITHSTANDING the ease with 
which Lamarckism appears to pro- 
vide the necessary machinery for the 
evolutionary process, this hypothesis 
is not free from serious defects. Dar- 
win considered it as a possible factor 
in evolution but did not lay much 
stress upon it. It was not until after 
Darwin’s time that Lamarckism came 
into prominence in consequence of the 
contrast between it and natural selec- 
tion. Half a century ago a new 
school, chiefly paleontological, arose 
which, under the name of neo-La- 
marckian, attempted to establish and 
expand the principles of Lamarck. 
This school was opposed by the neo- 
Darwinians who, under the leader- 
ship of Weismann, made a vigorous 
onslaught against Lamarckism and 


WHAT EVOLUTION IS 81 


claimed natural selection as the all- 
sufficient factor in evolution. 

The objections that were raised 
against Lamarckism by its opponents 
were first of all as to its limitations. 
As a process effective in evolution it 
applies to those changes that are in- 
duced either directly by the environ- 
ment or indirectly through exercise, 
lack of exercise, and the like. 

Some conditions seen in organisms 
do not easily fall under any of these 
heads. ‘The protective coloration of 
insects is an example of this kind. 
Many insects exhibit colors, forms, 
and activities that make them easily 
mistaken for other objects in their 
environment. Moths resemble the 
bark of the trees on which they rest, 
butterflies, on closing their wings, be- 
come indistinguishable from leaves 
or the earth and the walking-stick 
insect gets its name from its resem- 


82 WHAT EVOLUTION IS 


blance to twigs. Anyone who has 
taken the trouble to acquaint himself 
with examples of this kind must have 
been struck with the perfection of the 
resemblances and with the evident 
protection that the creature enjoys 
through being mistaken by its foes 
for something other than it is. It 
was this principle that toward the end 
of the Great War led to the camou- 
flaging of vessels, of artillery, and 
even of men. The insects that are 
camouflaged do not acquire this state 
through individual activity, but are 
hatched out in this condition. They 
receive their protective markings 
fully formed, in the nature of birth- 
rights as it were, and no efforts on 
their part make the camouflage more 
or less complete. In this respect, the 
insects are quite unlike the fishes, 
the frogs and toads, and especially the 
chameleons where the colors of the 


WHAT EVOLUTION IS 83 


skin are under nervous control, with 
the result, that the animals can mo- 
mentarily change colors and patterns 
and thus, so to speak, exercise this 
system as muscles may be exercised. 
In the insect the condition is fixed 
once for all and the individual is in- 
capable of modifying it. Fixed con- 
ditions of this kind are beyond the 
reach of the Lamarckian principles 
and form a body of material the evo- 
lutionary explanation of which must 
be sought for in other directions. 
Thus, granting the validity of La- 
marck’s hypothesis, it, nevertheless, 
falls short of an explanation of all 
the evolutionary aspects of organic 
nature and must be supplemented by 
other factors to reach completion. 
But not only does Lamarckism fail 
to apply to all classes of instances 
under organic evolution, it also in- , 
volves, as one of its essentials, the 


84 WHAT EVOLUTION IS 


assumption of the inheritance of ac- 
quired characters. Acquired charac- 
ters are those peculiarities that are 
gained during the lifetime of an in- 
dividual as contrasted with his inborn 
traits. That Lamarckism shall be 
effective, it is necessary that precisely 
these characters be inherited. For a 
long time biologists have attempted 
to show that such characters are in- 
herited, but thus far they have been 
unable to get any conclusive evidence 
that such is the case. 

The chief opponent of the inherit- 
ance of acquired characters was 
Weismann (1834-1914) who pointed 
out that the bodies of the higher ani- 
mals were composed of two catego- 
ries of cells, the body cells proper 
such as muscle cells, nerve cells, skin 
cells, and the like, and the reproduc- 
tive cells, the egg cells and sperm 
cells. He also showed that acquired 


WHAT EVOLUTION IS 85 


characters were changes in the body 
cells—muscle, nerve, skin and so 
forth—and that there was no known 
mechanism whereby the changes reg- 
istered in these cells could be trans- 
ferred to the reproductive cells in 
order that such changes might be 
handed on to the offspring. Ifa black- 
smith through exercise increases the 
muscles of his arm, how are these 
muscles to modify his reproductive 
cells that his offspring may have larger 
arm muscles than they otherwise would 
have had? This theoretic objection 
to the inheritance of acquired char- 
acters seems to many to be an insuper- 
able one, It is, however, an objection 
based on ignorance and may at any 
time be set aside by new discovery. 
Many of the older advocates of the 
neo-Lamarckian school pointed to the 
inheritance of mutilations as evidence 
in favor of Lamarck’s views, and it 


86 WHAT EVOLUTION IS 


was this that led Weismann and 
others to experiment in this direction. 
Colonies of mice and of rats were © 
subjected to mutilation and were 
then used for breeding with the view 
of ascertaining whether such mu- 
tilations were heritable. Thus the 
lengths of the tails of a number of 
adult white mice were measured, their 
tails were then cut off, and they were 
used as breeding individuals for a 
new generation. When the second 
generation had matured, their tails 
were in turn measured and cut off 
and a third generation was produced 
from them. After the breeding of 
approximately twenty such genera- 
tions, all of which had been subjected 
to the amputation of the tails at an 
appropriate stage, the tails in the final 
generation were found to be as long 
as those in the first generation. Such 
mutilations, then, gave no evidence 


WHAT EVOLUTION IS 87 


of being inherited and this conclusion 
was to have been expected at the out- 
set, for it is well known that the 
innumerable deformations of the hu- 
man body as practiced by primitive 
races whereby the ears, the lips, the 
nose, and even the head become mis- 
shapen, have had no inborn effect 
upon the stocks concerned. The an- 
cient religious rite of circumcision, 
though practiced for very many gen- 
erations by the Hebrews, has had no 
effect in shortening the foreskin of 
Hebrew male infants. If mutilations 
were inherited man would be a mere 
fragment of what he is as a result of 
handing on from one generation to 
another the injuries received from 
wars and accidents. Mutilations evi- 
dently are not inherited and the so- 
called examples of this kind seem to 
be nothing but old-wives tales or 
coincidences. 


88 WHAT EVOLUTION IS 


But even though mutilations have 
no effective influence on the germ 
cells of the animals suffering from 
such defects, may not bodily activi- 
ties, more normal in character than 
mutilations, influence the germinal 
elements? May not a normal but 
novel and unusual condition of the 
body cells influence the contained 
germ cells? To test this Castle and 
Phillips attempted the very ingenious 
experiment of transferring germ cells 
from one individual, with a given set 
of bodily traits, to another individual, 
with very different traits, and of test- 
ing the results of such a transfer by 
breeding. ‘They proceeded in the fol- 
lowing way. The ovaries were re- 
moved from a young guinea pig of 
pure white stock and in their place 
were set the ovaries from a pure 
black individual. After recovery 
from the operation, this white female 


WHAT EVOLUTION IS 8g 


with “black” ovaries was paired 
with a pure white male with the 
result that between six to twelve 
months after the operation she bore 
two litters of young. These consisted 
in all of six offspring every one of 
which was black exactly as though a 
black female had been paired with 
the white male. This test shows that 
after almost a year of residence in 
the foster white body the ovaries 
from the black female still retained 
in full force their original potentialt- 
ties and gave no evidence that the 
new foster body had influenced them 
in the least. This experiment sup- 
ports Weismann’s contention that the 
germ cells are essentially independent 
of the body in which they reside. 

But again it may be maintained 
that the period over which such trials 
extended was much too short for a 
real test of the question and that, if 


90 WHAT EVOLUTION IS 


experiments could be devised that 
would of necessity last over a number 
of generations, results of a very dif- 
ferent kind might be obtained. 

To try out this aspect of the prob- 
lem numerous investigations have 
been made or are still in progress. 
Few workers have done more in this 
direction than the Viennese experi- 
mentalist, Kammerer. Of his num- 
erous studies one may be chosen as 
an example. The European spotted 
salamander deposits either numerous 
eges or young that have been hatched 
in the mother’s body in ponds and - 
pools in damp woods. All the young, 
irrespective of their condition of 
birth, are provided with gills and 
live for several months in the water 
after which they lose their gills and 
become inhabitants of the land. The 
European black salamander gives 
birth only to active young, usually 


WHAT EVOLUTION IS gt 


two in number, and these are born 
without gills and in full readiness 
for terrestrial life. By keeping the 
spotted salamander away from water, 
Kammerer attempted to change its 
breeding habits in the direction of 
those of the black salamander. Such 
artificially restrained salamanders re- 
tained their young in their bodies till 
the young had lost their gills and 
were in a condition for life on the 
land. The young of such parents 
were reduced in number, as compared 
with the normal number produced, 
and were mostly black. In both these 
respects the stock approached the 
European black salamander. Spotted 
salamanders, whose parents had thus 
been modified in habit by experimen- 
tal conditions, on arriving at: sexual 
maturity were, during their breeding 
season, given access to water. They 
deposited their young in the water at 


92 WHAT EVOLUTION IS 


an advanced stage of growth, and 
these young remained in the water 
- only a few days instead of several 
months. Thus the reproductive hab- 
its of the spotted salamander, by a 
change in the environment, were 
modified in the direction of the black 
salamander, and this modification 
persisted more or less in their de- 
scendants, even after these descend- 
ants had been allowed to return to 
the original environment. 

Several lines of experimentation 
such as the one described in the pre- 
ceding paragraph have been carried 
out by Kammerer within the last few 
years and point to the inheritance of 
acquired characters. How sound the 
experimental evidence is in all such 
cases remains to be seen. Is it not 
possible that the peculiarities that 
Kammerer believed he originated in 
the spotted salamander, to take this 


WHAT EVOLUTION IS 93 


as an instance, may have been inborn 
traits in this animal which were 
simply called into evidence by the 
changed environment rather than 
produced by it? Certainly such as- 
pects of the problem should be tested 
before a final conclusion can be ar- 
rived at, and in so crucial an experi- 
ment as the one described, it 1s 
extremely desirable that independent 
evidence on the same point from 
other investigators should be at hand 
before a final decision is reached. 
Other students of this general 
problem have also carried out ex- 
tended series of experimental studies 
reaching over many generations. 
Thus the Americans Guyer and Smith 
have advanced evidence to show 
that eye defects produced in one 
generation of rabbits are inherited 
by the descendent stock. But here 
the defects produced and those as- 


04 WHAT EVOLUTION IS 


sumed to be inherited are often quite 
different and the question, therefore, 
of real inheritance remains open. 
The same general criticism applies 
to Griffith’s studies on the inheritance 
of defects in the internal ear of the 
rat. Both these lines of investiga- 
tion, and especially those of Guyer 
and Smith, are, however, extremely 
near the point and are very sugges- 
tive. 

A novel and very remarkable test 
of the inheritance of acquired char- 
acters is one that has been advanced 
by the celebrated Russian physiolo- 
gist Pawlow. It is well known that 
mice can be trained easily to come to 
a particular place for food. If, dur- 
ing this training, a bell is sounded 
each time that the animals are fed, 
they will learn after a while to come 
for food at the sound of the bell even 
when no other signal for the presence 


WHAT EVOLUTION IS 95 


of the food is given. This kind of 
response where a second form of 
stimulus, such as the sound of a bell, 
replaces the primary stimulus is called 
by Pawlow a conditioned reflex. To 
induce this state in untrained mice 
required, according to him about 
300 lessons. The descendants of this 
trained stock, however, acquired this 
capacity after only 100 lessons, the 
third generation after 30 lessons, the 
fourth after 10, and the fifth after 5 
lessons. Pawlow expressed the hope 
that in time a generation of mice 
might be produced in which this con- 
ditioned reflex would occur immedi- 
ately and, so far as that generation 
itself was concerned, without train- 
ing at all. These statements were 
published in a preliminary way in 
1923 and, though in certain respects 
they are very precise and final, it is 
hardly possible to comment on them 


96 WHAT EVOLUTION IS 


till the complete report is published. 
They are nevertheless full of signifi- 
cance. 

The whole problem of the inherit- 
ance of acquired characters has ar- 
rived at a stage where the results are 
coming to be of the first importance, 
and it must be admitted even by those 
who oppose Lamarckism that the re- 
cent tests have come much nearer 
yielding conclusive results than those 
attempted in the early stages of the 
controversy. Nevertheless lit is gen- 
erally agreed by almost everyone 
concerned that up to the present time 
no entirely convincing instance of 
the inheritance of acquired characters 
has come to light and that from this 
standpoint Lamarckism must be ad- 
mitted to be without direct support 
There are, however, those like Samuel 
Butler and, more recently, George 
Bernard Shaw, as disclosed in his 


WHAT EVOLUTION IS 97 


preface in “Back to Methuselah,” 
who cry out for Lamarckism, but 
their cry is far-fetched and although 
the Lamarckian doctrine may eventu- 
ally prove true, the proof of it will 
come from other sources than literary 
intuition. 

The conclusion that Lamarckism is 
a possible but unproved factor in evo- 
lution is a statement that represents, 
I believe, the opinion of the majority 
of modern biologists. That the criti- 
cism upon which this statement rests 
applies to animals only in so far as 
they exhibit sexual reproduction is, I 
suspect, generally appreciated though 
not so commonly stated. In organ- 
isms that reproduce in this way, as 
Weismann clearly showed, the cells 
that make up the creature are divisi- 
ble into the two classes of body cells 
and reproductive cells and, as already 
noted, it is extremely difficult, if not 


98 WHAT EVOLUTION IS 


impossible, to show how under such 
circumstances the inheritance of ac- 
quired characters can take place. In 
those forms in which non-sexual re- 
production is found the inheritance 
of acquired characters must be a reg- 
ular occurrence, for, in this method 
of reproduction, the whole body of 
the organism divides into two or 
more masses, and the body cells of 
the parent, with all the peculiarities 
that the environment may have im- 
pressed upon them, become the body 
cells of the offspring. Here the 
method of reproduction is as clearly 
in favor of the inheritance of ac- 
quired traits as in the other instance 
it is opposed to this process. It must 
be kept in mind, however, that non- 
sexual reproduction is a characteris- 
tic of the plants and the lower 
animals and is absent from the higher 
forms. It occurs on the animal side 


WHAT EVOLUTION IS 99 


among protozoans, sponges, corals, 
starfish, moss-animals, worms, and 
the group of sea-squirts or tunicates, 
but it is not known among: snails, 
clams, crustaceans, insects, or the ver- 
tebrates. If, therefore, the inherit- 
ance of acquired characters is a 
feature of non-sexual reproduction 
and the Lamarckian principles may 
apply where this occurs, it is after 
all a limited application and _illus- 
trates again what has already been 
pointed out that Lamarckism at best 
cannot be regarded as an all-inclusive 
factor in evolution. From what has 
been said it appears to be at best a 
possible element in this process. 


100 WHAT EVOLUTION IS 


4. DARWINISM 


DARWINISM, or as it is often called 
natural selection, is an explanation of 
evolution that originated independ- 
ently in the minds of Darwin and 
of Wallace. It is best stated in Dar- 
win’s memorable work “The Origin 
of Species” (1859), without doubt 
the most significant single publication 
of the nineteenth century. As a re- 
sult of the discussion called forth by 
the appearance of this work, two 
great steps in the progress of biology 
were accomplished; first, the accept- 
ance of descent with modification, 
instead of special creation as the 
order of organic nature, and, sec- 
ondly, the establishment of natural 
selection as a driving force in evolu- 
tion. The first of these has already 


WHAT EVOLUTION IS io1 


been taken up; the second remains to 
be considered. 

In seeking a clue as to the way in 
which evolution takes place Darwin 
first turned his attention to plant 
and animal breeding. Domesticated 
plants and animals, notwithstanding 
their great diversity and variety, are 
the products of comparatively few 
wild species. Thus all the various 
races of domesticated pigeons have 
descended from the European rock- 
pigeon. The original wild stock of 
this bird is fairly well represented by 
the common domesticated individuals 
of slaty color, with two dark bars on 
the wings and with a white rump. In 
addition to this stock there are over 
150 named varieties of pigeons that 
breed true. These include such un- 
usual forms as pouters, carriers, fan- 
tails, tumblers, jacobins, trumpeters, 
and a host of others whose forms and 


102 WHAT EVOLUTION IS 


habits are most diverse. Were these 
met with in nature, the zoologist 
would unhesitatingly assign many of 
them to separate species or even 
distinct genera. What is true of 
pigeons is also true of other domesti- 
cated animals such as dogs, horses, 
swine, cattle, and the like. 

In considering evolution Darwin 
first set for himself the task of ac- 
counting for the origin of domesti- 
cated stocks. He found that when 
the breeder wished to develop a par- 
ticular feature, such as an excessive 
covering of feathers on the leg and . 
foot of a pigeon, he watched his stock 
closely and chose for breeding pur- 
poses those individuals that showed 
evidences of the trait he sought. By 
this method of selection applied to 
one generation after another, he 
eradually arrived at a stock in which 
the given feature was as pronounced 


WHAT OEVOLUTION- IS: ‘103 


as he wished and thus attained his 
end. Darwin called this process arti- 
ficial selection and believed it to be 
the method by which man had pro- 
duced from comparatively few wild 
sources the great variety of domesti- 
cated forms with which he was sur- 
rounded. 

Darwin then raised the question, 
Is there not a similar process going 
on in nature as a means of producing 
the limitless variety of life in the 
open? This he believed to be so and, 
in contrast with artificial selection, 
he designated this process as natural 
selection. The grounds for his belief 
in natural selection as an actual proc- 
ess in nature may be briefly stated in 
the following way. _ 

More organisms are produced than 
can possibly continue to exist because 
of the limitations of food, space, and 
other essentials. This comes about 


104 ‘WHAT EVOLUTION IS 


from the fact that each individual or 
pair of individuals gives rise to sev- 
eral offspring and often to many. It 
is not always appreciated what this 
method of increase means. 

If a single plant produces at the 
end of its life two seeds and these 
grow to mature plants the next year 
and produce each two seeds and so 
on, in the twenty-first year the orig- 
inal plant will be represented by over 
a million descendants. Even an ani- 
mal, such as the elephant which 
breeds with extreme slowness, will 
nevertheless in time populate the 
elobe, if all its progeny live and re-. 
produce. When rapidly reproducing 
forms such as the insects are con- 
sidered, the increase in numbers is 
bound to be quickly prodigious so 
that the swarms of locusts described 
in the past seem as nothing to what 
might have happened. All organisms 


WHAT EVOLUTION IS 105 


are endowed with such powers of in- 
crease that even the slowest would in 
time overrun the earth. 

Darwin further recognized the 
fact that the offspring of all animals 
and plants are more or less diverse, 
and that no two are ever exactly 
alike. This is apparent to everyone. 
In a litter of puppies the individuals 
are quickly and easily distinguished 
by size, markings, vigor, disposition, 
and the like, and we name them and 
treat them as we do separate persons. 

These slight individual differences 
are, according to Darwin, either fa- 
vorable or unfavorable for the con- 
tinued life of the given organism and, 
since more individuals come into the 
world than can possibly survive, those 
with unfavorable traits are less likely 
to reach maturity and leave offspring J 
than those with favorable traits. In 
this way there is a continual elimi- 


106 = WHAT EVOLUTION IS 


nation of the less fit with the result 
that the fittest survive, leave off- 
spring, and thus hand on to future 
generations their peculiar qualities, 
for the individual differences noted by 
Darwin are the inborn traits of each 
individual. Thus a form of natural 
selection is continually in operation 
ever moulding plants and animals 
with great nicety to their fluctu- 
ating surroundings. This, according 
to Darwin, is the mainspring that 
keeps evolution continually moving. 
Survival of the fittest, struggle for 
existence, and other like expressions 
have been used as figures of speech 
with which to make clear what is 
meant by natural selection. And 
these expressions do indicate what at 
times occurs in nature, but anyone 
who looks upon the world of plant 
and animal life will not see a field of 
battle, an arena of combat, with each 


WHAT EVOLUTION IS __ 107 


living thing ranged against its neigh- 
bor. In fact when we seek a figura- 
tive expression for peace and quiet, 
we are very likely to turn to that very 
nature which, according to these 
phrases, should be in deadly turmoil. 
Nevertheless, natural selection is 
probably running at full speed in 
every quiet countryside. Four seeds 
from a given plant fall on a small 
plot of ground. All germinate and 
produce growing plants, one a little 
in advance of the other three. The 
early one shades the others, reaches 
maturity first and sets its seeds. Au- 
tumn comes and the other three have 
not yet flowered and in consequence 
they fail to produce fruit. Natural 
selection has taken place. The early 
plant leaves offspring for the next 
year; the other three are unrepre- 
sented. All may have lived what is 
essentially the same length of time 


1088 WHAT EVOLUTION IS 


and all in perfect peace; there has 
been no struggle, no conflict, but 
natural selection has nevertheless 
occurred. The essential act of re- 
production has been completed by 
only one and that one has thereby 
handed on its inborn peculiarities to 
the next generation. The same oper- 
ation is true of animals. Any crea- 
ture that fails to leave offspring 
suffers elimination from the stand- 
point of natural selection, yet such an 
animal or plant may live individually 
as long or even longer than many 
another whose progeny will reach 
into future generations. Hence na- 
tural selection is not necessarily con- 
cerned with the destruction of the 
individual, as is often inferred by 
the figurative expressions already al- 
luded to, but is a process that has to 
do with the way in which plants and 
animals succeed or fail in leaving off- 


WHAT EVOLUTIONS IS "109 


spring. In most instances it is a 
quiet, unobtrusive natural phenome- 
non that permeates nature in every 
direction and is more truthfully rep- 
resented by the quiet countryside than 
by the turmoil of battle. 

Having reached some idea of what 
is meant by natural selection or Dar- 
Wwinism and having seen how it may 
be an active force in moulding plants 
and animals, we may pause a moment 
to compare it with what Lamarck be- 
lieved to be the energizing factor in 
evolution. Natural selection first of 
all does not suffer from limitations 
to the extent that Lamarckism does. 
Natural selection not only applies to 
all that Lamarckism reaches but it 
meets with success such conditions as 
the protective coloration of insects, 
which, it will be remembered, were 
hardly within the range of Lamarck’s 
principle. Insects, that have only an. 


IO es WHATSE VOL TIGNaIS 


imperfect resemblance to the bark of 
the tree on which they rest, are much 
more likely to be espied and carried 
off as prey, than those that have a 
closer resemblance. Natural selec- 
tion may in this case be expected 
to act with full efficiency whereas 
Lamarck’s principle, as already indi- 
cated, is apparently entirely inappli- 
cable. From this standpoint, natural 
selection is not subject to the limita- 
tions that characterize Lamarck’s 
hypothesis. 

Further, natural selection is not 
concerned with the inheritance of ac- 
quired characters. The slight indi- 
vidual differences, upon which it is 
believed to act, are not differences 
due to the action of the environment 
on the given organism but are inborn 
traits which in consequence may be 
handed on through the germ cells to 
descendent offspring. In these two 


WHAT EVOLUTION IS 111 


particulars natural selection has a 
ereat advantage over Lamarckism. 
It is of wider application and it 
avoids the difficulty concerning the 
inheritance of acquired characters. 
It may not be amiss if at this point 
we compare Lamarckism and Dar- 
winism by attempting to show how 
each may be made to apply to the 
same example, and as an instance to 
to be so treated, we may take the 
webbed foot of the water fowl origin- 
ally discussed by Lamarck. Accord- 
ing to his hypothesis this structure 
arose by the accumulation, in the 
course of generations, of acquired 
modifications which resulted from a 
change of habit in consequence of the 
bird’s removal from purely terrestrial 
surroundings to an aquatic environ- 
ment. From Darwin’s standpoint the 
webbed foot resulted from selection, 
among a diverse offspring, whereby 


112 WHAT EVOLUTION IS 


those with favorable inborn traits 
would be preserved and have off- 
spring as contrasted with those whose 
conditions were less favorable. Thus 
Lamarckism deals with difference in- 
duced by the environment, acquired 
characters, and Darwinism with in- 
born native differences. 

Before leaving this comparison of 
the two views it should be pointed out 
that they are in no sense mutually ex- 
clusive. It is sometimes implied that 
if Darwinism could be shown to be 
true Lamarckism must be false and 
vice versa. It must be evident, how- 
ever, that such is not the case. There 
is not the least reason to assume that 
one view is in any way incompatible 
with the other. It is entirely possible 
that both Lamarckism and Darwin- 
ism may be acting at once and in per- 
fect accord as mutually efficient 
factors in evolution. 


WHat hVOCUTION IS. \113 


5. DARWINISM CRITICIZED 


In discussing Darwinism or natural 
selection from a critical standpoint 
we may begin by inquiring whether 
there is any evidence that this process 
is an actual occurrence in nature. To 
answer such a question, one would 
naturally turn to conditions where 
organisms are subjected to severe 
and unusual strain. Some years ago 
Bumpus studied the effects of a 
severe winter storm on sparrows. 
As a result of a heavy sleet many 
birds were brought close to death. A 
large number of these spent birds 
were collected, and of the total col- 
lection, 64 died and 72 revived. Do 
the members of these two groups 
thus naturally established differ, or 
are they essentially the same? A 
statistical study of the two sets of 


114, WHAT. EVOLUTION IS 


birds showed that the survivors were 
less variable than those that perished. 
The birds that died were, in many 
cases, extreme individuals. For in- 
stance, they more frequently had 
large bodies combined with small 
wings, or the reverse, than the sur- 
vivors had. Hence they represented 
conditions in which it might be said 
that there was too much power or too 
little power for the wing surface and 
the like. This disadvantageous ten- 
dency was in general the cause of 
their death. One may therefore con- 
clude that, under the severe circum- 
stances mentioned, elimination was 
not haphazard but rather, as would 
be expected, that the least fitted birds 
succumbed and the best fitted sur- 
vived. In this rather crude way, evi- 
dence of a selective capacity in nature 
has been obtained, and from instances 
of this kind, it is fair to conclude that 


WHAT EVOLUTION IS _ = 115 


natural selection is a process that is in 
actual operation in the world about us. 

Natural selection, however, is not 
without its limitations. It is an op- 
eration that at best can lift organ- 
isms only to the level of positive needs. 
Nature, with a certain prodigality, 
often goes much beyond this limit. 
Examples are abundant enough. 
Many crustaceans have the curious 
habit of casting injured legs and 
other appendages. When a crab loses 
a part of one of its legs, it recovers 
by a new growth, but this new growth 
does not replace simply the lost part; 
the old stump is thrown off from a 
so-called casting joint at the base of 
the leg and a wholly new leg is 
formed. Most crabs, picked up on 
the shore at random, are undergoing 
this process on some one of their nu- 
merous appendages. 

Hermit crabs live with the pos- 


/ 


116 WHAT EVOLUTION IS 


terior parts of their bodies tucked 
away in some dead snail-shell appro- 
priated by the crab for this purpose. 
Their hind appendages are therefore 
protected and, according to Morgan, 
who recorded this case, these append- 
ages are never found suffering from 
injury as their front legs are. Never- 
theless, if by experimental steps the 
hind appendages are injured, they are 
cast and recovered as the exposed 
appendages are. Here then is an in- 
stance where nature has stepped be- 
yond the actually necessary, and 
where it would be difficult to offer for 
the condition an explanation based 
purely upon natural selection. 
Another instance of the same kind 
occurs among certain almost micro- 
scopic crustaceans, the copepods. 
These small creatures are abundantly 
represented inthe surface watersof the 
sea. Copepods of different sexes are, as 


WHAT EVOLUTION IS 117 


a rule, strikingly unlike. The females 
are relatively inconspicuous and sim- 
ple in their dress. The males, on the 
other hand, are gaudy and ornamen- 
tal in the extreme. In their colors 
they are veritable microscopic pea- 
cocks. In fact the comparison with 
birds is quite appropriate, for just as 
the male bird often has a conspicuous 
plumage so is the male copepod com- 
monly highly decked out, and one 
would suppose for the same reason, 
namely, to attract the females at the 
breeding time. But the female cope- 
pod, unlike the female bird, has eyes 
that are quite incapable of taking in 
all this beauty, and we meet again a 
condition in which nature seems to 
have gone so far in excess of what is 
necessary that natural selection can- 
not be offered as a means of explaining 
the condition. This kind of excess, 
which is an example of what has been 


118 WHAT EVOLUTION IS 


called hypertely, is a common occur- 
rence in nature and is beyond the 
reach of natural selection. 

The most serious objection that 
has been raised against natural selec- 
tion is its apparent inability to launch 
any real change. When we consider 
how very slight and insignificant the 
individual differences are in any 
group of plants or of animals, it is 
almost inconceivable that these dif- 
ferences can afford sufficient grip for 
what natural selection is supposed to 
do in producing a new species. Once 
well established, it is easy to see how 
a new and advantageous trait can be 
fostered and developed by this proc- 
ess, but at the inception, it would 
seem impossible that natural selec- 
tion could start a new feature forward 
from such small beginnings. Indi- 
vidual differences are not sufficiently 
life and death differences to enable 


WHALE VOLUTION UES T19 


natural selection to obtain an initial 
hold. From the time of Darwin this 
has been the great obstacle to his 
theory, and no Darwinist has thus 
far successfully met this objection. 
When we view the face of organic 
nature, we see such an array of mar- 
velous adaptations and such a bewil- 
derment of plant and animal species, 
many of which are separated one 
from another by differences of a very 
slight kind, that we are forced to 
admit that it is inconceivable that 
natural selection, as understood by 
Darwin at least, could have produced 
what is before us. This conviction 
has so impressed itself upon the minds 
of most modern evolutionists, that 
they have one by one come to the con- 
clusion that natural selection, which 
in Weismann’s time was declared to 
be all-sufficient in evolution, may 
after all be of little real significance. 


120 WHAT EVOLUTION IS 


Opinions of this kind have been 
frankly expressed by such eminent 
authorities as Bateson in England 
and Morgan in America, and they 
reflect the view of the majority of 
biologists the world over. 

Although the statements of these, 
and other authorities on this subject, 
have been made with perfect clear- 
ness and in full knowledge of what 
the words imply, they have been 
seized upon by many thoughtless per- 
sons as evidence that biologists are 
abandoning the doctrine of evolution. 
What is really meant by these decla- 
rations, as must be evident to any- 
one who has read thus far, is that 
descent with modification, or evolu- 
tion, is not questioned, but that the 
particular explanation of it, known 
as natural selection, or Darwinism, is 
seriously doubted. One often sees in 
current literature lists of noted biolo- 


WHAT EVOLUTION IS 121 


gists who are said by anti-evolution- 
ists to be opposed to evolution, but, 
when the ground for these statements 
is scrutinized, it is commonly found 
that the authority named questions 
natural selection (Darwinism), but 
not descent with modification, or evo- 
lution, in the ordinary sense of the 
word. Ina recent newspaper a prom- 
inent Boston pastor names “some 
scientists who at least call in question 
the loudly asserted proof of evolu- 
tion.” These names include those of 
J. P. Lotsy and William Emerson 
Ritter both of whom have criticized 
Darwinism but, to the best of my 
knowledge, are firm believers in 
evolution. If by Paul Kamerer is 
meant Paul Kammerer and by E. B. 
McBride, E. W. McBride, the same 
statement applies to these zoologists 
as to the other two scholars named. 
Hence this list includes several well 


122 WHAT EVOLUTION IS 


reputed evolutionists. The confusion 
whereby these names have been in- 
cluded has probably arisen through 
failure to distinguish Darwinism from 
evolution. It is unclear thinking of 
this kind that is responsible for many 
of the present contentions. 

In the opening portion of this sec- 
tion, it was pointed out that natural 
selection was without doubt a real 
occurrence in nature, and as the dis- 
cussion progressed, it was made clear 
that this process, at least as under- 
stood by Darwin, fell short, and per- 
haps far short, of accomplishing 
what it was originally believed to do. 
This, 1n general, seems to be the 
modern opinion concerning it. That 
it is a real factor in evolution, there 
is not the least doubt; but that it is a 
subordinate factor, and perhaps even 
a very subordinate one, is likewise 
true. Biologists know that one spe- 


WHAT EVOLUTION IS 123 


cies comes from another, but how this 
is accomplished no one apparently 
can yet explain. As a contributing 
factor, natural selection doubtless had 
a hand in this operation, but it is in 
the rough-hewing of the species, and 
not in the polishing of the final prod- 
uct that itisconcerned. The polishing, 
which after all is perhaps the most 
essential aspect of the process, seems 
still to be hidden from scientific gaze. 


1244 WHAT EVOLUTION JS 


6. THE MUTATION , THEORY 


For almost forty years after the pro- 
mulgation of natural selection, biolo- 
gists were content to speculate on the 
way in which plants and animals 
might be changed through this prin- 
ciple. Only as the methods of zo- 
ology and of botany changed, from 
the more purely observational to the 
experimental, did evolutionary inves- 
tigation receive a new impulse. ‘This 
change in evolutionary work may be 
said to have been initiated, about the 
beginning of the present century, in 
the studies on heredity, carried out 
more or less independently by Tscher- 
mak, by Correns, and especially by 
de Vries. One of the results of these 
studies was the unearthing of the 
long-neglected but highly important 
publications of Mendel which had 


WHAT EVOLUTION IS | 125 


appeared some thirty years previ- 
ously. The principles, contained in 
Mendel’s writings, were at once 
made the basis of an extensive and 
thorough-going experimental pro- 
gramme and served, at the same time, 
as ground on which de Vries erected 
his mutation theory. 

Those portions of Mendel’s work 
that are directly concerned with 
the mutation theory are easily and 
quickly grasped. They can be illus- 
trated by what occurs in animals as 
well as in plants. If we breed a pure 
_ black guinea pig to a pure white one, 
the offspring are always black and if 
these offspring are bred amongst 
themselves, they produce young one- 
fourth of which are pure white and 
three-fourths are black. On testing 
the black individuals, one-third of 
them, or one-fourth of the total, can 
be shown to be pure black and the 


126 WHAT EVOLUTION IS 


other two-thirds, or one-half of the 
total, can be shown to be mixed, in 
that, like their parents, they will 
when bred together produce both 
black individuals and white individ- 
uals. The remarkable feature of 
such breeding series is the regularity 
with which the proportions, just 
stated, occur. The occasion of these 
remarkable Mendelian proportions 
can be seen when such a series, as 
that described, is analyzed. 

When opposing characters, such as 
white and black, are combined in 
breeding, as in the case of the guinea 
pigs mentioned in the preceding para- 
graph, only one of these characters 
appears in the first generation of off- 
spring, namely, in the particular in- 
stance under consideration, black. 
All guinea pigs in the first generation 
after the cross white-black are black. 
But these black individuals carry 


WHAT EVOLUTION HS: “127 


hidden in their bodies the white trait, 
for, when they are bred amongst 
themselves, one-fourth of their off- 
spring are white. Black, then, in 
some way overcomes white; not that 
it obliterates the white, but it holds 
this traitinabeyance. In the language 
of the modern breeder black is said, 
in a case such as the guinea pig, to be 
dominant over white and white is 
said to be recessive to black. This 
state of affairs, though not universal, 
is common to many such pairs of 
breeding characters. As a generali- 
zation, it is often referred to as the 
principle of dominance and was one 
of the discoveries of Mendel. 

A second and very much more im- 
portant principle, that is illustrated 
by the example under consideration, 
is, what may be called, the principle 
Oimthe = purity of, the céerm)It7is 
briefly this: a given germ cell, be it 


128 WHAT EVOLUTION IS 


sperm or egg, can carry the exciter 
or gene of only one of two opposing 
characters, such for instance as white 
and black. No germ cell can carry a 
gene for white and a gene for black 
at the same time. In any pair of op- 
posing traits, the gene of only one 
can be present in any germ cell. In 
other words the germ cells are in this 
respect always individually pure. 
This principle of the purity of the 
germ cell makes clear the remarkable 
proportions, already pointed out, in 
the second generation of offspring. 
It will be recalled in the example of 
the guinea pigs that, in the second 
descendent generation, there were one- 
quarter or twenty-five per cent pure 
whites, another quarter or twenty- 
five per cent pure blacks, and a half 
or fifty per cent black individuals 
which, however, were really mixed, 
for, on being bred amongst them- 


WHAT EVOLUTION IS __ 129 


selves, they, like their parents, pro- 
duced whites as well as blacks. 

If, now, we examine the whole 
breeding series from the standpoint 
of the purity of the germ, we shall 
find reason for the occurrence of the 

proportions given. This can be done 
best by reference to the diagram on 
page 131. Here it will be seen that 
the source of the descendent stock 
is the pair of guinea pigs, one white 
and the other black, represented in 
outline at the top of the page. Which 
of the two is male and which female 
makes no difference so far as the final 
outcome is concerned. The white one 
is supposed to have been derived 
from a pure white stock, that is, 
from a stock which in all its pairings, 
within its own bounds, produced 
nothing but white individuals. Hence 
the white pig must be assumed to 
have come from an egg containing a 


130 WHAT EVOLUTION IS 


white gene, fertilized by a sperm also 
containing a white gene. This is rep- 
resented in the diagram by the two 
white circles above the white pig, one 
for the egg and the other for the 
sperm. Such an individual can pro- 
duce only one class of germ cells, 
namely those with white genes. As- 
suming in this particular instance 
that the white pig is the female, she 
may then be described as an individ- 
ual producing eggs all of which carry 
the white gene. If the white member 
of the pair is the female, the black one 
must be the male and what has been 
said of the white pig may be said of 
her black mate, except that black gene 
is to be used in place of white gene 
and sperm cell in place of egg cell. 

In the first descendent generation 
all offspring, in the present instance, 
would be the product of a white egg 
fertilized by a black sperm. This is 


WHAT EVOLUTION IS 


Guinea-pig 
e@ 00 


Four-o'clock 
ee foXe) 


131 


, 


GPa f 
Aes Wat 
Panty, inky ,) { 





WHAT: EVOLUTION IS 133 


indicated by the white circle and the 
black circle in the diagram over the 
representative of this generation. In 
consequence of the dominance of 
black over white, all individuals, in 
this generation, will have black coats. 
But since they arise from a germinal 
mixture, each of these individuals 
will be able to produce two kinds of 
germ cells, the males white sperm and 
black sperm, and the females white 
eges and black eggs. If, now, we 
assume that the two kinds of eggs 
are produced in equal numbers and 
that the same is true of the sperm and 
that the union of egg and of sperm is 
purely fortuitous, the kinds of guinea 
pigs and their proportionate num- 
bers, as already stated for the second 
descendent generation, will be ex- 
' actly realized. For with two kinds of 
sperms and two kinds of eggs, there 
will be four possible combinations in 


134 WHAT EVOLUTION IS 


fertilization. Once in four chances 
a white sperm will fertilize a white 
egg, a process which will yield the 
twenty-five per cent pure white guinea 
pigs. Once in four a black sperm 
will fertilize a black egg and thus will 
arise the twenty-five per cent pure 
black guinea pigs. Once in four a 
white sperm will fertilize a black egg 
and once in four a black sperm will 
fertilize a white egg and these two 
classes taken together will yield the 
fifty per cent mixed stock which, like 
their parents, can produce either 
white or black offspring. Thus the 
assumption of the purity of the germ 
leads to a simple and illuminating 
understanding of the proportionate 
numbers of young in the several Men- 
delian classes. 

This assumption has been tested by 
geneticists in many ways and has been 
found to hold good. In fact, the 


WHAT EVOLUTION IS 135 


whole set of Mendelian principles has 
proved in the hands of the experi- 
mentalist little short of marvelous in 
their application. Exceptional cases 
often occur, but when these are 
worked out, they are commonly found 
to be in essential agreement with the 
general principles. Thus when the 
red-flowered variety of the common 
garden four o’clock is crossed with 
the white-flowered form, as shown 
on the lower half of page 131, the off- 
spring are neither red-flowered nor 
white-flowered but have flowers of an 
intermediate tint, pink. If now these 
offspring are bred amongst them- 
selves three classes result: twenty- 
five per cent pure whites, twenty-five 
per cent pure reds, and fifty per cent 
pinks, a state of affairs that may be 
described as parallel to that of the 
guinea pigs, so far at least as purity 
of the germ is concerned but without 


1336 WHAT: EVOLUTION IS 


dominance. In this way particular 
examples may show individual dif- 
ferences and thus illustrate the extent 
to which the general principles are 
open to readjustment. 

De Vries, having discovered inde- 
pendently much that was afterwards 
found in the writings of Mendel and 
having come to many of the same 
conclusions that this writer had ar- 
rived at, turned to the problem of 
evolution in the hope that the new 
ideas on heredity would be helpful in 
understanding descent with modifi- 
cation. In 1901 he published the first 
general account of his mutation 
theory. According to this theory, the 
characters by which we distinguish 
different plants and animals are made 
up of units which are sharply sep- 
arated from one another and are 
without intergrades. They are repre- 
sented by such features as black and 


WEA EVOLUTION IS) 137 


white in the guinea pig’s coat. These 
opposing traits were called unit or 
elementary characters by de Vries 
and, in describing them as elementary, 
he meant that they partook in their 
separateness of the nature of the 
chemical elements. Every organism 
is marked by a great array of these 
unit characters. In the guinea pig, 
for instance, there are coat colors, 
white, black, piebald and the like, dif- 
ferences in hair, long, short, rosetted, 
or smooth, and a host of other features 
all of which are inherited in accord- 
ance with Mendelian principles. 
Thus the pairs of traits in Mendelian 
inheritance are the unit characters of 
the mutation theory. 

According to de Vriesa real species, 
or as he called it an elementary species, 
is to be described from its unit char- 
acters and any new combination of 
unit characters is a new species. A 


138 WHAT EVOLUTION IS 


black guinea pig differs from a white 
guinea pig in one unit character, and 
yet this is sufficient to place these two 
individuals in different elementary 
species. This is certainly a novel 
conception, for it implies that two 
brothers may be of diverse species 
provided they show a unit character 
difference. In evolution, however, 
we are not so much concerned with 
this aspect of the subject as with 
another. 

As already stated, the unit char- 
acters, by which elementary species 
may be distinguished, show no inter- 
erades; they are fixed characters. 
Hence the difference between one ele- 
mentary species and another is an 
abrupt difference. These abrupt dif- 
ferences are what de Vries calls muta- 
tions, and he contrasts them with 
the very slight individual differences 
which are seen between members of 


WHAT EVOLUTION IS = 139 


the same species and which are com- 
monly designated as variations. Vari- 
ations, according to de Vries, are 
always very slight and insignificant. 
They never even approximate the 
magnitude of a mutation. Mutations 
on the other hand are striking differ- 
ences such as black or white in the 
coat of a guinea pig and represent, 
in this sense, considerable jumps or 
breaks. Variations are like the slight 
movements that a cube may be made 
to execute when it is wabbled about 
on one of its faces. Mutations are 
like the changes that arise when 
the cube is turned from one face to 
another. 

The mutation theory is to the effect 
that evolution takes place not through 
small differences or variations, as Dar- 
win believed, but through large and 
sudden changes, mutations. Just as 
the cube does not progress when it 


140 WHAT EVOLUTION IS 


merely wabbles back and forth on one 
side, so evolution makes no progress 
through variations. Only when mu- 
tations occur, when the cube rolls over 
on to a new face, is evolution taking 
place. Darwin recognized mutations 
as conditions in nature and used for 
them the breeder’s common name of 
sport. He was doubtful, however, 
whether they had any significance in 
evolution. To de Vries they are 
the only real factor in evolutionary 
progress. 

No one can have bred plants or an- 
imals for any length of time without 
having noticed the frequency with 
which mutations occur. Morgan, in 
his exhaustive study of inheritance in 
the fruit fly, has recorded many scores 
of mutations, and there is no reason 
to suppose that they do not occur as 
frequently in open nature as in the 
laboratory. 


WHAT EVOLUTION IS_ 141 


Whether a mutation persists or not 
depends upon its nature. If it is in 
a favorable direction, the individual 
possessing it is likely to be preserved 
and finda mate. As such changes are 
handed down undiminished by Men- 
delian inheritance, the mutation would 
be expected to reappear in many of 
the descendants in full vigor. In this 
way, it could establish itself in the 
stock and help to modify that stock so 
as to form a new species. As de Vries 
rightly states, this process of preser- 
vation involves natural selection, for 
the retention of such a character de- 
pends upon this principle. All muta- 
tions must run the gantlet of natural 
selection. In this sense, the mutation 
theory and natural selection are 
mutually dependent. The mutation 
theory yields the grain for the natural 
selection hopper. 

It must be evident that the muta- 


i 


142° (WHAT EVOLUTION] Ts 


tion theory presents a means of avoid- | 
ing the chief difficulty with which 
Darwinian natural selection has to 
contend. That difficulty, it will be 
remembered, had to do with the first 
steps in the origin of favorable traits. 
These steps are not necessary in the 
origin of mutations, for mutations 
appear fully formed and are not built 
up by slow degrees. This is the great 
advantage that the mutation idea has 
over Darwin’s view of the way in 
which new traits are supposed to be 
ushered in. As mutations they enter 
fully formed. 

Difficulties with the mutation the- 
ory can be easily found. First of 
all this theory depends upon Men- 
delian inheritance and what that kind 
of inheritance implies as to the sep- 
arateness of characters. But char- 
acters often blend, in fact there may 
be such a condition as blended in- 


WHAT EVOLUTION IS)? (143 


heritance, and such a condition, if at 
all general, would be very restricting 
to the mutation view. 

Mutations further give the impres- 
sion of laboratory and of garden 
products, rather than of products of 
the land and sea. Mutations certainly 
occur in nature, witness albino ani- 
mals, but the experimental product 
seems to be far removed from what 
is demanded by open nature. Many 
workers have been so impressed with 
this aspect of the question, that they 
have come to look upon the great 
biological advance of the last two 
decades as illuminating, from the 
standpoint of heredity, but as having 
very little real bearing on the evolu- 
tion problem. The truth is that the 
mutation idea, and all its intricate 
connections, are somewhat too novel 
to admit of final judgment. 

What the factors of evolution are, 


144. WHAT EVOLUTION IS 


what the moving forces behind this 
great natural process are, no one is 
in a position to state. Lamarckism 
may be one of these. Darwinism 
alone, or supplemented by the muta- 
tion idea, seems quite clearly another 
though perhaps a subordinate one. 
Others still are probably to be dis- 
covered, for it is unlikely that a proc- 
ess so intricate, so many-sided, and 
so far-reaching as organic evolution 
should depend for its energizing on 
only one source. 


My 
HUMAN APPLICATIONS 





HUMAN APPLICATIONS 


MAN as an animal is a product of evo- 
lution and is subject to its laws as all 
other animals are. Such a statement, 
however, does not mean that man with 
all his complexities is at once under- 
stood the moment this position is as- 
sumed. The evolutionary standpoint, 
like a mountain top, is a commanding 
situation for a general survey, but it 
does not do away with the intricacies 
in the field of vision, it merely brings 
them into more truthful relations with 
the whole. 

The derivation of civilized man 
from a primitive human stock is a 
subject that has grown so enormously, 
in the last few decades, that its treat- 
ment merits a volume. The new in- 
formation on the subject, that has 
come to us since Darwin’s time, is 


148 WHAT EVOLUTION IS 


simply overwhelming in amount. Man 
appears to have been on the earth for 
nearly half a million years. His old- 
est known representative is from Java, 
the Trinil man or Pithecanthropus, 
a restoration of whose head has been 
made by McGregor. This is shown in 
an outline sketch at the top of page 149. 
For the use of this sketch and the 
other outlines of heads on this page, 
I am indebted to Professor R. S. Lull 
and to the Yale University Press. 
Pithecanthropus flourished about 
500,000 years ago and is believed to 
have made use of fire and simple flint 
implements. — 

Of later date is the dawn-man, 
Eoanthropus, of Piltdown, England, 
who lived about 250,000 years ago. 
His bones seem to be the most ancient 
remains of man in England and occur, 
associated with crude stone imple- 
ments and the remains of several 


WHAT EVOLUTION IS_ 149 





Trinil man Piltdown man 





Neandertal man Cré-Magnon man 


vo 
ys ay 
wh Py," 


ACE 
iP 


Ho Cee 
cone 


J 


vera 
, Wee wh Viet 


4? fe ¢ J 
CPN ] Aq. 
I i 





Viera y ORU TIONS Soro r 


animals long since extinct. Another 
ancient type of man is the Neandertal, 
or Mousterian man, evidences of 
whom have been found in many Euro- 
pean localities. These remains date 
from about 100,000 years or more 
ago. Of still later time is the Cro- 
Magnon man, believed to be of the 
same species as ourselves. His period 
may be set at some 25,000 years ago, 
and his blood may still flow in the 
veins of certain European peoples. 
He was remarkable for his great 
height, being commonly over six feet 
tall. His stone implements were of 
good workmanship, and his engrav- 
ing, painting, and sculpture show him 
possessed of esthetic traits and of 
unusual powers of expression. His 
remains have been found in Wales, 
France, and Spain. These few ex- 
amples show how rich and numerous 
are the traces of primitive man. 


152 WHAT EVOLUTION IS 


That man has descended from an 
ape-like stock no reasonable person 
can doubt. He shows this affiliation 
in his body and in his activities in a 
thousand ways, and yet more than 
most animals, he has peculiarities of 
his own. When we look at civiliza- 
tion as represented in the complex life 
of cities and of nations with all their 
commercial interrelations, with their 
humane institutions such as asylums 
and hospitals, and with their oppor- 
tunities for intellectual, esthetic, and 
spiritual growth, it seems as if an 
attempt to base this enormous struc- 
ture on an evolutionary foundation, 
with Lamarckism, Darwinism, and 
the like as driving forces, is futility 
in the extreme. Who for a moment 
would attempt to account for the 
Divine Comedy as a product of evolu- 
tion? And yet, if evolution means 
anything, it means exactly this. Some- 


WHAT EVOLUTION IS 153 


where in the scope of its totality evo- 
lution must finda place for the highest 
achievements of the human soul, or the 
general conception crumbles. Every 
thorough-going evolutionist believes 
this and looks to the natural history of 
man, when viewed in its all-inclusive 
light, as the real history of man. 

But how is it that man holds such 
an exceptional place in the world? 
We are quite sure that never before 
in the history of the earth has there 
arisen an organism that has probed 
the universe as man has, that has 
developed art, poetry, religion, and 
science as the human species has done 
and is doing to-day. Not that these 
accomplishments are in any sense 
final or ultimate, for no one can tell 
what the future has in store, but com- 
pared with the efforts of the long 
geologic past they are stupendous. 
We look with admiration on the bee 


134 WHAT EVOLUTION IS 


and the ant, and we are astounded at 
the instinctive capabilities of many 
animals, but, when we examine our- 
selves closely, we find most of these 
potentialities within us and a host 
more of capacities of which no lower 
creature seems ever to have dreamed. 

In what respects has man lifted 
himself so much above his neighbors? 
Man 1s first of all a social organism. 
He is banded together in families, 
clans, and nations and, as thus organ- 
ized, he resists the vicissitudes of life 
vastly more successfully than he pos- 
sibly could single handed. As an 
organization, human society is in 
many respects unique. Social life was 
tried eons ago by the simpler animals 
in a thousand different ways; proto- 
zoan colonies out of which sexuality 
grew, sponge colonies and coral col- 
onies which have had a hand in mould- 
ing the earth’s surface, insect colonies 


WHAT EVOLUTION IS 155 


such as the ant hill and the bee swarm, 
all these preceded human society by 
untold ages. Wheeler informs us 
that in the insects alone social states 
have arisen no fewer than twenty- 
four different times in as many dif- 
ferent groups of these animals. Yet 
none of these societies accomplished 
what man, as a social organism, has 
achieved. 

They almost all differ from human 
society in two fundamental aspects. 
First of all, the members of most 
animal societies are close-blood rela- 
tives. In the ant hill the individuals 
are commonly the offspring of one 
queen; they are all sisters in one 
household. In almost all animal col- 
onies, except the human, this close- 
blood relationship holds. Second, 
among the colonies of lower animals 
the division of labor is relatively 
slight. In human society occupations 


156 WHAT EVOLUTION IS 


mount into the tens of thousands at 
the very least. Among the other co- 
lonial animals the classes of perform- 
ance are to be counted at most in 
scores. In the beehive, the drones 
have as their one duty the fertiliza- 
tion of the queen, the queen is service- 
able only in that she lays eggs, and 
finally the worker performs the ordi- 
nary duties of caring for the young, 
procuring food, cleaning the hive and 
the like. Compare for a moment the 
relative simplicity of even so complex 
a situation as that in the beehive with 
the enormous intricacies of human 
life and civilization, where blood- 
relationship is most diverse and per- 
formance is specialized to an almost 
incredible degree. These aspects of 
human society set it in strong contrast 
with the social organizations of all 
other animals. 

Another feature, in which man 


WHAT EVOLUTION IS 157 


differs from most animals, is in his 
striking ability to use the environment 
to his advantage. The primitive ac- 
quisition of fire made available to 
him such gigantic forces as we see in 
steam, electricity, and their endless 
applications. Who would have sus- 
pected that the unclad savage, as he 
warmed himself over the dying em- 
bers, was nursing a form of energy 
that was to do for man all that modern 
machinery has done! Little do we 
think as we look at a watch face that 
shines in the dark that the changes 
going on there foreshadow, in germ, 
possible sources of energy for future 
man that may be as much superior to 
fire as fire was to ancient brawn. But 
this may be so, and it is precisely this 
capacity to discover and utilize to the 
utmost such environmental changes 
that makes man different from almost 
all other organisms. 


158 WHAT EVOLUTION IS 


In harnessing the energies of nature 
man has discovered and perfected 
tools. Few other animals use tools. 
Monkeys and apes have their sticks 
and stones, but it took man to fash- 
ion them into serviceable shapes, 
to discover metals, to build engines, 
steamships, and airplanes. Man’s 
tools were amongst his first posses- 
sions and not till he acquired the habit 
of preserving them and passing them 
on to future generations did society 
progress. The race that buries with 
the primitive artisan the choice ob- 
jects of his life’s work never goes 
forward. Even the rude tools of one 
generation must be put in the hands 
of the next, if real progress is to be 
made. In this sense the inheritance 
of property separates man from most 
other animals. 

Another trait in which man is pe- 
culiar is in the possession of a com- 


WHAT EVOLUTION IS __1s9 


plex language. The lower creatures 
have their cries as outlets for emo- 
tional states, and these cries form 
a simple kind of organic language. 
Everyone knows the difference be- 
tween the hum of a complacent and of 
an angry bee. How diverse and in- 
forming are the vocal sounds of a 
dog. All these are types of primitive 
language, but they are almost end- 
lessly remote from human _ speech 
which, as represented in written form, 
is not only a means of communica- 
tion between distant individuals but 
the stabilizer of all past events, the 
vehicle of history. From this stand- 
point the simple organic language 
of the lower animals fades into in- 
significance. 

Finally, though not last, for there 
are many other points of contrast be- 
tween man and other animals, the 
human species has acquired the habit 


160 WHAT: EVOLUTIONS 


of teaching, of passing on to a new 
generation the practices and the wis- 
dom of the older generations. This 
is largely a human institution, for few 
animals other than man possess the 
least trace of it. Very many animals 
learn. Beasts, birds, frogs, and fishes 
learn; even an earthworm can learn 
to find its way out of a simple maze. 
Such animals learn by individual ex- 
perience; they do not learn by ex- 
ample. To learn by example is to have 
a model and this is at once the worth 
and the artificiality of the teacher. 
Man learns not only by experience as 
the lower animals do, but also by 
being taught and the profession of 
teacher is almost exclusively a human 
profession. Contrary to the belief of 
the commonalty, animals, other than 
man, do very little teaching. In a 
beehive worker bees, that have never 
seen a queen reared, will make queen 


WHAT EVOLUTION IS 161 


cells and hatch queens with as much 
skill as the best. Their operations are 
largely instinctive. Such perform- 
ances are not taught, though bees like 
most animals of their grade can learn. 

Thus, man, though an animal, is 
preeminent in a multitude of ways as 
compared with his neighbors. He has 
the most intricate and complicated 
form of social life of which we have 
any knowledge. He controls his en- 
vironment, devises and uses tools, and 
acquires property as no other organism 
has ever done. He has developed a 
most complex spoken and written lan- 
guage which serves him for com- 
munication and record, and he teaches 
as wellas learns. No wonder with all 
these exceptional traits that he ap- 
pears so strikingly unlike other ant- 
mals. It is therefore to be expected 
that his evolutionary relations will be 
far from usual. 


162 WHAT EVOLUTION IS 


When we ask ourselves how im- 
portant natural selection is in human 
affairs, and whether man’s life pro- 
gresseswithno showofthe inheritance 
of acquired characters, we pass im- 
mediately into a situation where every- 
thing that the biologist has taught 
seems to be contradicted. At every 
step human society seems to have 
gone forward by the inheritance of 
daily acquisitions and all our humane 
institutions, charities, and the like cry 
out against such an ideal as natural 
selection. ‘This reversal of affairs is, 
however, merely apparent. 

Every scheme in evolution, whether 
it be Lamarckian or Darwinian in its 
tendencies, turns on the transmission 
of traits, on heredity, and when we 
inquire what and how man inherits, 
we find him as peculiar in this respect 
as he is in others. A child may in- 
herit, for instance, a book from its 


WHAT EVOLUTION IS _ 163 


parent which means that this partic- 
ular book is passed from the parent 
dead to the child living. This is the 
literal significance of the term inherit. 
But less tangible things than a book 
may be inherited; the child may in- 
herit the parent’s habits of thrift and 
frugality or of poor table-manners. 
Such an inheritance involves learning 
through example and applies to an 
enormous number of social customs. 
Finally the child may inherit the color 
of the parent’s eyes or his stature or 
the like, and this form of inheritance, 
which involves a rather figurative use 
of the term, we know to be germinal. 
The eyes, unlike the book, are not 
handed on from parent to child, but a 
tendency is transmitted whereby the 
child’s eyes develop the color of those 
in the parent. This tendency, as we 
know, is passed on by the egg or the 
sperm. Almost no other animal than 


164 WHAT EVOLUTION IS 


man inherits as we inherit a book, and 
few animals inherit as we do thrift or 
table-manners, but all animals inherit 
as we inherit eye-colors and the like. 
This type of inheritance has been 
called germinal, or organic, and may 
be contrasted with the other types of 
inheritance which have been called 
social, for they depend primarily on 
man’s social condition. Human in- 
heritance, then, like other human 
capacities, is more complex than in- 
heritance in lower animals, for it in- 
cludes in addition to their type of 
inheritance, social inheritance. 
Organic or germinal inheritance 
involves the physical traits of our 
bodies, hair-color, eye-color, size, 
tendencies and resistances to disease 
and, less physical in character, tem- 
perament and the like. Many of these 
peculiarities are inherited in accord- 
ance with Mendelian principles; they 


WHAT EVOLUTION IS 165 


are subject to mutational change and 
to natural selection. The part La- 
marckism plays in their moulding is 
as little known in man as in other 
animals. 

Social inheritance includes our so- 
cial customs, our language and the 
way we use it, our daily habits of 
honesty or dishonesty, frugality or 
wastefulness, and such minutiae as 
eating food with a knife or using a 
napkin. All these features are learned 
either through experience or from a 
teacher. None of them comes to us 
through the sperm or the egg. Lan- 
guage, one of the most fundamental, 
never reaches us as a germinal con- 
tribution, but must be learned by each 
generation as it matures. To these 
traits natural selection has no applica- 
tion except in a figurative way, for 
though an individual may gain a mate 
and offspring in consequence of his 


166 WHAT EVOLUTION IS 


table-manners, there 1s no certainty 
that any of his descendants will show 
these traits as they may his eye-color 
or hair-color. Social inheritance is 
accomplished on what may be de- 
scribed as a Lamarckian model, for 
the habits of one generation are modi- 
fied and, as such, are handed on to the 
next. But this, of course, is through 
what one individual learns from an- 
other and not through the germ, so 
that when we speak of it as La- 
marckian we are using that term in 
a figurative way. 

The methods of social inheritance, 
then, are very different from those of 
germinal inheritance. They have a 
superficial resemblance to the La- 
marckian conception, and probably it 
is this resemblance coupled with our 
great familiarity with them in daily 
life that predisposes us to the La- 
marckian doctrine. It is a strange 


WHAT EVOLUTION IS = 167 


fact, but nevertheless true, that in the 
estimation of character or in the for- 
mation of friendships we are more 
likely to be influenced by social than 
by germinal inheritances. The color 
of the hair or the color of the eye is 
under such circumstances of less 1m- 
portance to us than the speech or table- 
manners. ‘Thus human inheritance 
and in consequence human evolution 
extend over a wider field than the 
corresponding operations in lower an- 
imals and man’s uniqueness again re- 
asserts itself. 

But though we are in this respect 
above the rest of creation, we are still 
subject to the common law. Not an 
epidemic sweeps through a commu- 
nity without leaving behind it, in the 
young members of the population, a 
selected race whose partial immunity 
will have its effect on the coming gen- 
eration. This is especially noticeable 


168 WHAT EVOLUTION IS 


in the arrival of a new disease. The 
first coming of Europeans to America 
is said to have brought to the native 
Indian a variety of entirely novel mal- 
adies. Among these was smallpox. 
This disease is said to have run like 
wildfire among the natives and to have 
reduced their numbers to an almost 
incredible level. Measles is another 
disorder of the same kind. To the 
Aleut Indians, of the extreme North- 
west, this is a disease of great severity 
and has been known to have exter- 
minated whole villages. Yet to Eu- 
ropeans it is a mere bagatelle due 
doubtless to the long exposure of this 
race to it and to the partial immu- 
nity acquired in the course of time 
through selection. 

The social habits of man have not 
only had their influence on the kinds 
of inheritance that he has developed, 
but they have impressed his nature 


WHAT EVOLUTION IS: 169 


and in fact that of every other social 
organism, in a way too often over- 
looked. All such organisms are of 
necessity cooperative. It is inconceiv- 
able that a social state should exist 
otherwise; in every sound state there 
must be cooperation between its mem- 
bers. In fact the so-called solitary 
animals show more or less coopera- 
tion, and it is this primitive condition 
that reaches a much higher level 
of development in all social forms. 
Wheeler has very justly emphasized 
this feature in the life of the insects. 
It is commonly overlooked that, among 
most animals, cooperation is as usual 
a form of response as competition, 
and in social organisms, it is of neces- 
sity a primary form of response. 

In consequence of his social pro- 
clivities, we find, in the evolution of 
man, a large body of permanent al- 
truistic action which in the form of 


170. WHAT: EVOLUTION MS 


benevolent acts, charities, and the like, 
is intended to extend the life of those 
who otherwise might meet a speedy 
end. Viewed from what might be 
regarded as a biological level this 
practice at first sight would seem to 
demand condemnation. Why not fol- 
low the example of the ant and destroy 
all defectives? Surely this would give 
added resources to those who are most 
able to use them. But a wholesome 
human society could not exist under 
such circumstances. Such an act as 
the destruction of the weak would be 
so subversive of the cooperative prin- 
ciple, not to mention the higher vir- 
tues, that a state endorsing such a 
practice would disintegrate and fall. 
This principle is so clearly recognized 
that civilized man has always striven, 
and rightly striven, to succor the un- 
fortunate. 

Yet if one takes the trouble to look 


WHAT EVOLUTION IS 171 


through any group of public hospitals 
or asylums, he cannot help but be im- 
pressed with the heavy burden of 
wreckage there represented. In a 
harsh world natural selection would 
have removed much of this, but the 
hand of public benevolence has inter- 
vened and warded off the stroke. 
_ Nevertheless, every one must see that 
if such a weight as this be sufficiently 
increased, society may be crushed by 
it. The situation is not an academic 
one, but has already begun to bear 
heavily on legislatures and through 
them on the public. What may be 
done to meet, in a humane way, such 
a situation? That the state should ar- 
range for those who, in their weak- 
ness, come upon it as public wards to 
live the length of life that nature 
allots them is indisputable. But that 
such individuals should be restrained 
from perpetuating their kind is like- 


1720 “WHAT EVOLUTIONS 


wise reasonable. It will probably soon 
come to be a recognized function of 
the state to guard against offspring 
from those of its wards who, because 
of serious heritable incapacity, are on 
its hands. How this is to be accom- 
plished — through segregation, steril- 
ization, or some other effective means 
—is a practical question that com- 
munities may sooner or later be called 
upon to settle. In the performance of 
this duty society, like natural selec- 
tion, will concern itself not so much 
with the life of the individual as with 
what that life may transmit to future 
generations. 

Thus man’s nature though in many 
respects apparently contradictory to 
that of the animals below him is after 
all grounded on the same basic prin- 
ciples. He has evolved far beyond 
the vast majority of creatures and 
though he has reached a level where 


WHAT CEVOLUTION AS: 173 


conduct is directed in new ways and 
under novel conditions, he is never- 
theless still subject to the old laws. 
There is after all only one kind of life 
in the universe. 


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VI 
READING REFERENCES 





READING REFERENCES 


Darwin, C. 
The Origin of Species, 1859. 
Many subsequent editions. 
De Vries, H. 
Die Mutationstheorie, 1901-1903. 
De Vries, H. 
Species and Varieties. Their Origin 
by Mutation, 1905. 
LAMARCK, J. B. 
Philosophie Zoologique, 1809. 
LaMARCK, J. B. 


Zoological Philosophy. Translated by 
H, Elliot, 1914. 


Caste, W. E. 

Genetics and Eugenics, 1924. 
ConkKLIN, E. G. 

Heredity and Environment, 1919. 
Lu ti, R. S., H. B. Ferris and others. 

The Evolution of Man, 1922. 
Morcan, T. H. 


A Critique of the Theory of Evolution, 
1916. 





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